MANUAL  OF  LITHOLOGY: 


TREATING    OF 


THE  PRINCIPLES  OF  THE  SCIENCE 


WITH    SPECIAL    REFERENCE    TO 

MEGASCOPIC   ANALYSIS, 


BY 

EDWARD   H.    WILLIAMS,  JR.,  E.M.,  F.G.S.A., 

Professor  of  Mining  Engineering  and  Geology, 
Lehigh  University,  South  Bethlehem,  Pa. 


WITH     SIX     PLATES 


SECOND    EDITION. 
FIRST  THOUSAND. 


NEW    YORK : 

JOHN    WILEY   &    SONS. 
LONDON     CHAPMAN    &    HALL,    LIMITED 
1899. 


COPYRIGHT,  1895, 

BY 

EDWARD  H.  WILLIAMS,  Ji 

\AT 


A 


firaunworth,  Mnnn  ^f  Barber, 

Priuters  and  Bookbinders, 

16  Nassau  Street,  Brooklyn,  N.  Y. 


PREFACE  TO  THE  SECOND  EDITION, 


THE  microscope  has  forced  lithology  and  petrography 
so  widely  apart  that  the  layman  is  often  at  a  loss  to  recog- 
nize old  acquaintances  under  new  names.  This  edition  of 
Lithology  is  written  on  the  same  basis  as  the  last  —  for  the 
beginner  in  the  subject  who  wishes  a  thorough  knowledge 
in  the  megascopic  presentation  of  the  subject,  in  a  fuller  and 
more  compact  arrangement  than  can  be  obtained  in  geologi- 
cal text-books.  It  is  also  designed  for  the  engineer  who 
wishes  to  understand  the  valuation  of  rocks  for  economic 
purposes.  The  arrangement  is  such  that  those  who  wish 
to  continue  the  work  in  the  microscopic  analysis  of  rock- 
forming  minerals,  as  taught  in  petrography,  will  have 
nothing  to  unlearn.  The  reader  is  supposed  to  have  a 
practical  acquaintance  with  megascopic  crystallography 
and  mineralogy,  the  use  of  the  blowpipe,  and  the  ordinary 
methods  of  chemical  analysis,  so  that  these  subjects  are 
merely  touched  upon  in  the  description  of  the  more  com- 
mon megascopic  rock-forming  minerals.  An  addition  has 
been  made  in  the  line  of  the  economic  value  of  rocks,  and 
the  body  of  the  book  has  been  entirely  rewritten,  and  is 
from  five  to  six  times  the  size  of  the  former  edition,  so  rap- 
idly has  the  subject  grown.  Credit  has  been  given  for  data 
taken  from  other  authorities. 

E.   H.  W.,  JR. 
LEHIGH  UNIVERSITY,  July  22,  1895. 


TABLE  OF  CONTENTS. 


PAGE 

INTRODUCTION,  .        ,        -        .        .        .       '.»...        .  .          i 

PRELIMINARY  DESCRIPTION,  .        .        .        .        .        .        .        .        .  6 

ROCK-FORMING  MINERALS,        .        .        ...       .        .        .  ,      .        .  .        14 

GENERAL  DEFINITIONS,          .     ••;        .        .        .        .        ...      .         .,  55 

THE  ROCKS,      .        .        .        ...        „        .        .    x '   .        .  .        92 

Primary  Rocks,            .         .         .         .         .         .         .         .      •  .'       .  97 

Acid  Division — Mica  Rocks,        .         .         %        .         .         ....  107 

Rhyolite-granite  Series,        .         .         .         .         .         .         .          ,  107 

Intermediate  Division — Amphibole  Rocks,          .         .         .         .  .       144 

Trachyte-syenite  Series,        .                   ......  145 

Phonolite-elaeolite-syenite  Series,    .         e         .         .                   .  158 

Mica-trap  Series,         ,.         .         .                  .         .                  .         .  174 

Porphyrite  Series,    .    -               .         .                            .         .         .  .       178 

Andesite-diorite  Series, 182 

Basic  Division — Pyroxene  Rocks,       .        '.         .         .         .         .  .213 

Nephelinite-iolite  Series,      .         .         .         .         .         .         .        .  214 

Feldspathoid  basalts,        .         .         .         .         .         ,         .         .  .       217 

Tephrite-basanite-theralite  Series,        .                  .         .         ...  221 

Basalt-gabbro  Series,       .         .         ^        .         .         .         .         ,  .       225 

Extrusives,        .       "»         .        •.         ...         .         .         .  225 

Plagioclase  Group,            ,  J      .         .        ,         .         .         ,  .       226 

Olivine  Group,       '         .         „         .         .         .         .         .        .,  233 

Pyroxene  Group,      .         .         »         .        ,        i         .         .  ;       234 

Intrusives,         ..         ,.         .         .         .         ,.         .  234 

Plagioclase  Group,            .         ,         ,  "      »         .         .  .       235 

Olivine  Group,       .       -.         .         ,         *         .,'       „         .         .  249 

Pyroxene  Group,      .         •        .        .        .         .       . .         ,  .       252 

Magnetite  Group,          .         .        •         .       '"»         .         .         .  252 

Secondary  Rocks,           .        .         . 255 

Debris  Division,       .         •         .  .       .         .         .         .         .         .         .  259 

Sedimentary  Division,        •         •         •         .         .         .         .  t       265 

Metamorphic  Division,    ........  324 

Contact  Series, ^30 

Acid  Series,          ••••.-....  330 

Basic  Series,    .         .         .         .         .          .         .         .  nee 

Minerals  as  Rocks,     ........  371 

SCHEME  FOR  DETERMINING  THE  PRINCIPAL  ROCKS,        .        .         .  382 

ECONOMIC  VALUE  OF  ROCKS, 39<2 

INDEX  OF  AUTHORITIES,           ••••....  401 

GENERAL  INDEX 4O5 

v 


MANUAL  OF  LITHOLOGY. 


INTRODUCTION. 

THE  tendency  of  modern  rock  analysis  is  toward  a 
simplification  of  the  subject,  and  the  discarding  of  useless 
and  misleading  divisions  and  names.  At  present  there 
seems  to  be  a  reaction  against  separating  dike-forms  of 
rocks  from  their  massive  states,  the  attempting  to  dis- 
tinguish rocks  on  account  of  geological  age,  and  the  basing 
a  rock  name  on  a  chemical  bulk  analysis.  The  tendency  in 
metamorphism  is  backward  to  the  old  theories  of  primary 
origin,  and  "  eruptive  "  gneiss  is  no  longer  a  misnomer  to 
many.  It  seems  necessary  to  faintly  outline  the  present 
state  of  belief  of  petrographers  on  some  of  the  above  sub- 
jects, so  that  the  reason  for  the  arrangement  chosen  in  this 
book  can  be  understood,  and  the  first  subject  will  be  in 
regard  to  dike-rocks.  This  state  is  produced  whenever  an 
eruptive  is  forced  into  or  through  a  fissure  whose  walls  are 
approximately  parallel  to  one  another.  Depending  on  the 
depth  of  the  fissure  below  the  surface,  its  walls  will  be  of 
varying  temperatures,  and  the  fluid  mass  will  be  cooled 
correspondingly  rapidly  or  slowly ;  but,  whether  slowly  or 
rapidly,  the  bulk  of  the  intruded  mass  will  be  slight  when 
taken  transverse  to  the  cooling  surfaces,  and  the  crystal- 
lization, at  best,  will  not  reach  the  development  that  obtains 
in  larger  masses  that  cool  more  slowly  ;  so  that  dike-cooling 


2  MANUAL   OF  LITHOLOGY. 

will  give  smaller  sized  grains.  If  the  cooling  is  slow  and 
the  walls  heated,  there  may  be  a  uniformity  of  grain  across 
the  fissure ;  but  the  fact  that  the  mass  has  been  cooled  before 
becoming  stagnant  at  the  point  of  consolidation  will  only 
allow  a  uniformly  small  grain  to  form.  This  even  grain  has 
been  taken  as  a  dike-facies  when  it  depends  on  the  heating 
of  the  dike-walls  to  a  degree  corresponding  to  the  temper- 
ature of  the  intruded  mass;  and  that  is  caused  by  the  fissure 
being  deep-seated  enough  to  be  within  the  heated  abysses, 
or  by  so  long  a  passage  of  the  hot  magma  through  the 
fissure  that  the  country-rock  has  been  heated  to  a  great 
distance.  This  presupposes  an  escape  of  the  magma  at  the 
surface  readily  during  the  first  part  of  the  flow  ;  or  tne  in- 
fluence of  the  walls  would  have  cooled  the  mass  and  plugged 
the  fissure.  We  need,  therefore,  a  hot  liquid  lava  and  a  free 
escape  at  the  surface  for  the  first  portions  of  a  flow  resulting 
in  a  final  stagnation  that  crystallizes  evenly  across  the  dike. 
It  is  seen  at  once  that  all  dike-flows  cannot  follow  this 
sequence,  owing  to  narrowness  of  fissure  or  coolness  of 
lava ;  so  that  only  some  dikes  have  this  facies.  We  find  a 
similar  facies  along  the  peripheries  of  bosses  and  large  lac- 
coliths; so  that  it  is  not  due  to  the  shape  of  the  cooling 
magma,  but  to  the  rapidity  of  cooling. 

A  late  eminent  authority  objected  to  claiming  so  great 
a  metamorphic  power  for  dikes,  and  especially  for  dike- 
granite.  He  stated  that  the  great  effect  of  metamorphism 
shown  in  the  country  of  the  dike-walls  was  not  due  to  the 
granite  (which  was  probably  a  trachyte  when  intruded),  but 
to  a  subsequent  regional  metamorphism  that  affected  both 
dike  and  walls,  altering  the  former  to  granite,  and  the  latter 
to  its  present  condition.  It  would  be  sufficient  to  quote  the 
words  of  Dr.  Barrois  that  regional  metamorphism  and  con- 
tact metamorphism  are  much  the  same  thing ;  but  in  this 
case  there  is  a  misapprehension  that  will  extend  to  others 


IN  TROD  UCTION.  3 

and  create  a  wrong  impression.  In  answer  it  may  be  said 
that  it  is  more  probable  to  imagine  the  extent  of  the 
metamorphism  due  not  to  the  fact  that  the  granite  is  in 
the  dike  form,  but  to  the  fact  that  dike-walls  are  some- 
times heated,  as  above  described ;  that  this  heating  from 
passing  hot  fluid  produces  the  metamorphism,  and  the 
stagnant  fluid  crystallizes  uniformly  and  sharply  up  to  the 
dike-walls.  Against  the  argument  of  a  metamorphosed 
trachyte  may  be  advanced  the  statement  that  the  latter 
supposition  would  not  account  for  the  sharpness  of  the 
dike-walls,  as  regional  metamorphism  of  a  nature  that 
would  produce  the  necessary  mineral  zones  in  the  aureola 
would  more  or  less  obliterate  the  walls,  or  cause  a  shading 
from  the  granite  facies  to  that  of  the  metamorphosed  walls, 
and  such  changes  are  not  found.  It  may  also  be  advanced 
that  it  does  not  require  a  greater  amount  of  heat  to  meta- 
morphose the  walls  in  the  one  case  than  in  the  other,  and 
that  it  is  as  easy  to  suppose  the  walls  heated  before  the 
stoppage  of  the  flow,  either  by  the  length  of  time  during 
which  the  flow  passed,  or  from  the  fact  that  the  whole 
region  was  heated  to  a  point  just  below  metamorphism  (by 
orogenic  or  other  causes)  before  the  fracture  and  intrusion 
took  place,  and  that  the  intrusive  supplied  the  needed 
increment  for  metamorphism.  It  is  also  difficult  to  see  how 
regional  metamorphism  would  produce  an  aureola  and 
zones  about  a  cold  dike  of  trachytic  habit,  and  not  extend 
generally  through  the  mass. 

The  attempt  to  separate  dike-rocks  from  those  filling 
plugs  is  still  more 'hard  to  understand,  as  both  begin  and  end 
alike,  differ  only  in  shape,  and  contain  similar  fillings.  Dike- 
rocks  are  generally  accepted  as  fillings  of  fissures  which 
may  have  reached  the  surface  and  through  which  extrusives 
passed.  Lapse  of  time  has  allowed  those  surface  states  to 
be  denuded,  and  we  have  only  the  filled  vent. 


4  MANUAL   OF  LITHOLOG  Y. 

The  credit  of  destroying  the  idea  that  rocks  can  be 
separated  according  to  geological  age  belongs  in  a  high 
degree  to  American  geologists.  If  we  take  the  mixture  of 
mica,  quartz,  and  feldspar  which  forms  the  rhyolite-granite 
series,  we  are  asked  to  believe  that  the  quartz-porphyries 
.are  the  extrusives  of  the  granite  in  the  past,  and  the  rhyo- 
lites  in  the  present.  We  find  quartz-porphyries  as  late  as 
the  Eocene  (in  Elba);  and  the  late  G.  H.  Williams  found  in 
the  Archaean  area  of  the  South  Mountain  along  the  border- 
line of  Pennsylvania  and  Maryland  pre-Cambrian  rhyolites 
devitrified  and  altered,  but  retaining  lithophysas  and  flow 
structure.  These  two  examples,  which  demolish  the  hypo- 
thesis in  this  group,  are  parallelled  in  other  groups,  so  that 
the  American  and  English  authorities  do  not  allow  group- 
ings according  to  fancied  geological  ages. 

Bulk  analyses  of  rocks  are  given  in  the  books  on  the 
subject,  and  rock  groups  created  from  chemical  differences. 
The  researches  of  Lang  conclusively  show  that  nothing  can 
;be  thus  based,  as  the  same  rock  will  show  a  varying  bulk 
analysis  when  fresh  and  weathered,  and  the  same  mineral 
group  will  vary  widely  in  the  components  of  a  bulk  analysis  ; 
while  rocks  of  varying  mineral  composition  will  agree 
closely  in  bulk  analyses.  The  rock  groups  of  the  future 
must,  therefore,  depend  more  on  mineral  than  chemical 
composition.  While  the  majority  of  authorities  define  an 
*'  acid "  rock  as  one  whose  bulk  analysis  shows  a  certain 
percentage  of  silica,  Lessing  says  that  it  is  one  that  carries 
a  surplus  of  silica  after  saturating  the  bases,  no  matter  how 
great  or  small  that  may  be.  The  terms  "  acid  "  and  "  basic  " 
.are  indefinite  terms,  and  bulk  analyses  are  misleading. 

.Sorby's  theory  of  differentiation  of  magmas  is  rapidly 
pushing  its  way  to  the  front  as  a  new  basis  for  dividing 
rocks,  though  how  that  is  to  be  done  is  not  yet  sufficiently 
plain.  The  theory  as  modified  by  Iddings  is  finding  quite 


IN  TROD  UCTION.  5 

general  acceptance,  and  the  work  of  the  future  may  be 
devoted  to  the  study  of  Judd's  "  petrographic  provinces.'" 
It  is  possible  that  differentiation  will  finally  take  the  subject 
out  of  the  hands  of  the  average  student,  and  that  it  will  be 
understood  only  by  the  expert  with  a  microscope.  It  is  a 
matter  of  congratulation  that  the  familiar  rock  names  have 
been  left  in  the  majority  of  cases,  so  that  there  is  little  to  be 
unlearned  as  the  science  progresses.  In  general  it  may  be 
said  that  modern  progress  has  been  towards  simplicity  of 
arrangement. 

In  the  following  pages  many  rocks  based  entirely  on 
microscopic  distinctions  have  been  given  for  the  purpose  of 
making  this  a  complete  book ;  but  in  every  case  there  is  a 
distinction  between  what  can  be  seen  by  the  eye  (with  a 
lens)  and  by  the  microscope.  The  symbol  (M)  will  be  used 
for  whatever  can  be  seen  by  the  eye,  and  will  be  equivalent 
to  "  megascopic,"  "  by  the  eye,"  etc.,  while  the  lower-case 
(m)  will  be  equivalent  to  "  microscopic,"  "  by  the  micro- 
scope," etc.  In  rock  definitions  these  symbols  will  be  freely 
used,  as  well  as  in  the  discussion  of  states  and  varieties  of 
rocks  and  forms  of  minerals. 


PRELIMINARY  DESCRIPTION. 

Geology  is  the  discussion  of  the  history  of  the  earth,  and 
of  its  life,  from  the  earliest  times.  Geognosy,  or  structural 
geology,  is  that  branch  which  deals  with  the  components  of 
the  earth,  their  arrangement  to  form  its  structure,  and  the 
development  of  the  latter.  The  materials  can  be  separated 
into  the  envelope  (air  and  water)  and  the  litho  sphere.  It  is 
with  the  latter,  principally,  that  structural  geology  has  to 
do,  and  this  solid  portion  can  be  considered  in  two  ways: 
(i)  as  formed  of  individual  rocks  ;  (2)  as  arranged  in  masses 
or  beds  to  form  terranes  (as  used  by  J.  D.  Dana ;  terrain  of 
C.  D'Orbigny).  Lithology  is  that  division  of  geognosy  which 
treats  of  the  rocks  of  the  lithosphere  as  mineral  aggregates, 
under  all  conditions  of  hardness,  and  all  states  of  aggregation 
and  consolidation.  Aggregates  totally  lacking  consolidation 
are  included  ;  so  that  loose  bodies  (as  sand,  clay),  viscoids 
(as  asphalt,  ice),  organic  bodies  (as  peat,  guano),  hard  bodies 
(as  granite,  trap) — all  are  rocks.  According  to  Lang,  a  rock 
is  an  individual  product  of  an  uninterrupted  rock-forming 
process.  An  eruptive  rock  is  formed  at  a  single  earth-throe  ; 
a  secondary  rock  is  formed  from  an  eruptive  by  an  uninter- 
rupted action  of  natural  forces.  To  fully  understand  rock 
origin  it  will  be  necessary  to  include  some  definitions  of 
terrane  structure,  as  well  as  some  theories  of  the  constitution 
of  the  earth's  interior.  In  distinction  to  lithology,  there  is 
a  second  method  of  studying  rocks  by  the  microscope.  This 
is  more  of  a  mineral  analysis  than  lithology,  and  bears  to  it 
exactly  the  same  relation  that  chemical  analysis  and  blow- 


PRELIMINARY  DESCRIPTION.  7 

pipe  reactions  do.  It  investigates  the  origin  of  the  rock  as 
well  as  its  composition,  and  is,  therefore,  a  higher  branch  of 
the  subject,  called  petrography. 

Rocks  are  mineral  aggregates,  and  may  be  simple,  when 
formed  necessarily  of  one  mineral,  or  composite,  when  made 
up  of  two  or  more  different  ones.  Rock  definitions  should 
contain  only  the  necessary  and  essential  components,  and  all 
accessory  minerals  should  be  placed  in  the  following  dis- 
cussion. Necessary  ingredients  give  the  name  to  rock  classes : 
"  A  granite  is  composed  of  quartz  and  feldspar."  Essential 
ingredients  mark  rock  species  ;  as  the  addition  of  hornblende 
to  the  above  makes  hornblende  granite  ;  the  addition  of  augite, 
•augite-gramte.  Accessory  ingredients  are  local  in  their  oc- 
currence, or  inconsiderable  in  amount ;  but,  when  more  than 
usually  abundant,  may  form  rock  subspecies  ;  as  the  presence 
of  considerable  hypersthene  in  augite  granite  makes  hyper- 
•f^^-augite-granite ;  or  an  abundance  of  garnets  in  mica- 
schist  makes  garnetiferous  mica-schist.  Necessary  and  es- 
sential ingredients  may  be  further  defined  by  saying  that  a 
change  in  the  former  would  throw  the  rock  into  another 
class,  and  in  the  latter  into  another  species.  A  rock  may 
have  the  same  mineral  as  necessary  and  accessory,  or  as 
-essential  and  accessory ;  as  quart '^-schist  must  necessarily 
have  quartz ;  but  veins  of  quartz  traversing  such  a  schist 
are  but  the  filling  of  a  fracture  that  may  run  into  adjoining 
rocks  of  a  different  composition,  and  are,  therefore,  only 
in  the  slightest  degree  accessory.  In  the  resolution  of 
pyroclasts,  or  a  partly  solidified  magma  at  depths  in  the 
«arth,  there  may  be  mineral  components  more  resisting 
than  the  bulk  of  the  mass,  and  these  will  float  in  the 
magma  and  be  etched  (corroded)  by  it ;  or  in  the  case  of  an 
intratelluric  crystallization  before  differentiation,  or  the 
eruption  of  magmas  of  different  composition  through  the 
same  vent  and  at  the  same  time,  there  may  be  a  similar 


8  MANUAL   OF  LITHOLOGY. 

placing  of  the  intratelluric  phenocrysts  in  a  bath  differing 
from  the  one  in  which  they  formed,  and  a  similar  etching 
will  result.  M-Levy  and  Fouque  apply  the  term  allogenic 
to  all  crystals  formed  at  such  different  periods  as  would  cover 
the  first  supposition  ;  but  the  term  will  not  apply  to  those 
similar  ones  formed  through  corrosion  in  a  differentiated 
portion  of  the  same  mass.  Minerals  may  also  be  classed  as 
primary  and  secondary.  The  former  are  crystallizations  from 
the  original  magma  before  solidification ;  the  latter,  due  to 
causes  acting  after  solidification.  These  causes  may  be  : 

(a)  Growths  about  the  original  grains  or  crystals,   by 
which  fetsites  have  been  devitrified  and  changed  to  quartz- 
porphyries  ;  sandstones  have  been  altered  to  quartzites,  as 
at  Bethlehem,  Pa., — in   this   case   the  growths   are  of   the 
same  mineral  material. 

(b)  Growths  of  different  mineral  matter  about  crystals  to 
form  paramorphs. 

(c)  Infiltrations  from  the  country-rock,  or  from  the  interior 
of  the  rock  itself,  which  crystallize  in  the  openings  of  the 
rock  (vesicles,  pores,  cavities,  fissures,  cracks,  joint  planes, 
etc.)  to  form  amygdaloids,  druses,  geodes,  nests,  strings,  etc., 
as  agate,  zeolites. 

(d)  Replacements  of  mineral  matter  without  changing  the 
form   of   the   original   mineral,  as  pseudomorphs,  as   in   the 
pyritiferous  porphyry   of    Leadville,    where   pyrite   forms 
pseudomorphs  after  hornblende  and  biotite. 

The  following  definitions  and  classifications  are  based  on 
work  with  the  unaided  eye  (megascopic  analysis),  though  an 
appeal  to  the  microscope  will  be  taken  in  the  discussion  of 
the  theories  of  rock-formation  ;  but  before  entering  upon 
them  it  is  necessary  to  touch  upon  that  branch  of  lithology 
which  treats  of  the  individual  components  of  rocks,  mineral- 
ogy, as  far  as  the  description  of  the  species  common  to  rocks, 
and  called  rock-formers,  and  the  manner  in  which  they  occur 


PRELIMINARY  DESCRIPTION.  9 

in  rocks.  The  student  in  mineralogy  pays  attention  to  the 
crystallographic,  optical,  physical,  and  chemical  characters 
of  the  mineral  as  an  individual,  crystallizing  with  freedom, 
and  uninfluenced  by  association  with  others  in  process  of 
formation.  If  exceptions  occur,  they  are  noted  as  foreign 
to  the  usual  habit.  Mineralogy  from  a  lithological  stand- 
point is  another  study,  as  all  of  the  minerals  which  are  rock- 
formers  must  of  necessity  mutually  influence  one  another ; 
so  that  the  first  thing  to  be  noted  is  the  shape  in  which  the 
mineral  will  be  found  in  rock  masses.  The  next  thing  of 
importance  is  a  method  of  isolating  mineral  species  for 
inspection  or  analysis.  The  only  method  of  inspection  here 
treated  is  by  the  pocket  lens.  The  blowpipe  and  chemical 
tests  are  the  same  as  in  mineralogy.  It  is  well  to  note  that 
the  rapidity  of  response  to  the  latter  depends  on  the  ratio  of 
the  extent  of  surface  exposed  to  the  volume  of  the  mineral. 
This  increases  with  the  extent  of  comminution;  so  that 
powdered  forms  are  most  quickly  acted  upon  by  solvents. 
In  crushing  specimens  for  chemical  tests  the  powder  should 
be  fine  enough  to  ensure  definite  and  rapid  reaction ;  for 
physical  tests  the  product  must  retain  as  sharp  an  outline 
and  as  great  freedom  from  dust  as  possible.  A  rough  crushing 
through  rolls  frequently  separates  the  component  minerals 
in  grains  of  various  sizes,  and  these  can  be  separated  by 
classification  through  screens.  Woven  wire  can  be  procured 
with  a  mesh  of  I-.2  mm.,  and  bolting-cloth  of  various  grades 
to  still  finer  sizes.  Screens  need  not  exceed  2^-3  inches  in 
diameter.  A  tinsmith  can  make  a  series  of  screen-frames  for 
a  field  outfit  that  can  be  readily  renewed  at  any  time,  though 
the  wear  is  insignificant.  Make  a  template  by  turning  one 
end  of  a  piece  of  oak  two  inches  square  and  six  inches  long 
to  form  a  cylinder  two  inches  in  diameter,  and  a  scant  half 
inch  long,  and  have  the  tinsmith  solder  half-inch  wide  strips 
of  light  tin  so  as  to  exactly  fit  the  cylinder.  Make  the  same 


IO  MANUAL    OF  LITHOLOGY. 

number  of  small  cylinders,  of  the  same  length  and  \-^  inch 
greater  diameter.  Place  a  smaller  ring  on  the  template,  and 
cut  from  the  screen  material  a  circle  four  inches  in  diameter. 
If  it  be  of  bolting-cloth,  lay  it  centrally  over  the  ring,  and 
slip  over  cloth  and  ring  one  of  the  larger  rings,  and  drive 
down  with  a  few  taps  of  a  light  hammer.  The  cloth  will  be 
stretched  and  retained  between  the  two  rings,  and  when 
worn  out  can  be  replaced  by  a  new  piece.  In  the  case  of 
the  wire  cloth  the  edges  must  first  be  bent  over  the  template 
with  the  fingers,  and  then  placed  as  above  described.  This 
series  of  screens  can  be  arranged  from  coarse  to  fine  above 
one  another  by  procuring  tin  cylindroids  (slightly  conical) 
two  inches  long,  with  the  larger  end  fitted  to  the  outside  of 
the  screens,  and  the  smaller  end  to  the  inside  of  the  same. 
Any  number  of  screens  can  thus  be  arranged  in  a  set,  and 
the  ends  of  the  top  and  bottom  ones  closed  by  caps,  so  that 
no  dust  will  escape  on  shaking  a  mixture  placed  in  the  upper 
and  larger  screen.  On  separating  the  screens  each  will  hold 
the  next  larger  class,  and  these  may  be  sorted  in  any  one  of 
the  many  varieties  of  laboratory  sorters  with  ascending 
currents.  The  most  common  way  is  to  use  a  solution  of 
some  salt  which  gives  a  definite  and  high  specific  gravity. 
The  requirements  of  such  a  solution  are  that  it  shall  be  as 
harmless  as  possible  ;  that  it  shall  be  stable  under  ordinary 
conditions  of  temperature  ;  that  it  shall  have  no  effect  on  the 
minerals  separated ;  that  they,  in  turn,  shall  not  react  upon 
it ;  that  diluting  it  will  not  alter  its  composition ;  and  that 
evaporation  will  bring  it  back  to  its  condition  before  dilution. 
D.  Klein,  in  1881,  proposed  a  solution  that  now  bears  his 
name,  which  fulfils  the  above  conditions,  and  can  be  diluted 
with  water.  There  are  other  solutions  of  different  sp.  grs.; 
but  they  require  some  other  diluent,  are  less  stable,  or  are 
noxious.  Kleins  solution  is  formed  by  dissolving  a  very 


PRELIMINARY  DESCRIPTION.  II 

soluble  borotungstate  of  cadmium  in  slightly  less  than  ten 
per  cent,  of  its  weight  of  water  at  22°  C.  At  15°  C.  it  has  a 
sp.  gr.  of  3.28  ;  but  by  evaporating  over  a  water  bath  till 
oli vine  floats  in  the  warm  solution  it  has,  on  cooling,  a  sp. 
gr.  of  3.6.  By  adding  water  the  gravity  can  be  reduced  to 
any  required  figure,  and  evaporating  will  restore  it  again. 
In  using  this  or  any  other  solution  that  can  be  changed  by 
•dilution,  and  when  a  certain  sp.  gr.  is  to  be  obtained,  we 
place  on  the  surface  a  considerable  fragment  of  a  mineral 
with  density  slightly  greater  than  that  desired,  and  dilute 
by  single  drops  till  the  mineral  sinks.  It  must  be  kept  in 
mind  that  a  number  of  circumstances  may  affect  the  result, 
and  that  the  sorts  may  not  be  exactly  what  we  think  them 
to  be ,  as  (i)  the  buoyant  effect  of  a  liquid  increases  quite 
rapidly  with  fineness  of  crushing,  as  is  well  known  in  ore- 
dressing  ;  (2)  the  buoyant  effect  is  greater  in  highly  cleavable 
minerals  (micas)  than  in  others  of  the  same  density  that 
break  in  other  forms  ;  (3)  minerals  frequently  hold  other 
minerals  as  inclusions ;  (4)  the  fragments  may  be  mixtures 
of  widely  varying  minerals,  so  arranged  as  to  have  a  medium 
density ;  (5)  incipient  weathering,  metachemism,  etc.,  may 
have  set  in.  Minerals  with  magnetic  properties  can  be  re- 
moved from  the  rock  powder  by  a  magnet  (magnetite, 
pyrrhotite,  etc.). 

The  value  of  chemical  analyses  depends  on  how  they  are 
made — whether  "  bulk  analyses,"  where  the  sum  of  the  ele- 
ments or  their  oxides  for  the  whole  rock  is  obtained  ;  or  each 
mineral  is  isolated  as  far  as  possible  and  its  composition 
learned.  It  has  been  long  known  that  there  was  too  much 
variation  in  the  silica  and  other  ingredients  of  rocks, — granite, 
for  example, — to  allow  a  "  type  analysis "  to  be  adopted, 
and  lately  the  majority  of  authorities  have  abandoned  the 
attempt  to  reconstruct  the  mineral  character  of  a  rock  from 


12  MANUAL    OF  LITHOLOGY. 

its  chemical  bulk  analysis,  as  many  rocks  of  greatly  varying 
mineral  composition  have  nearly  the  same  bulk  analysis. 
Iddings  is  quoted  as  saying  that  the  variations  in  the  rapidity 
of  cooling  the  fluid  mass  cause  the  variations  in  mineral 
composition,  independent  of  the  pressure  exerted.  Bulk 
analyses,  therefore,  should  be  used  with  caution,  and  as 
checks,  or  for  purposes  -of  comparison ;  as  a  fresh  and 
weathered  fragment  of  the  same  rock,  and  taken  from  places 
adjacent  to  one  another,  will  give  greatly  varying  bulk  an- 
alyses, and  might  throw  the  specimens  into  different  species 
were  they  to  be  taken  alone. 

The  examination  of  mineral  powder  of  varying  coarseness 
can  best  be  made  on  paper,  using  a  color  strongly  contrast- 
ing with  that  of  the  powder — unless  specimens  of  it  are  to  be 
preserved,  and  those  can  be  mounted  on  glass  slides  with 
Canada  balsam.  Microchemical  tests  can  be  made  in  the 
field  with  a  good  lens  and  glass  slides,  and,  following  the 
suggestion  of  Bolton,  a  bottle  of  finely  powdered  citric  acid 
should  be  carried  for  acid  tests  (carbonic  acid),  which  can  be 
applied  to  the  streak  of  the  rock,  or  its  powder  placed  on 
glass  and  both  wet.  A  solution  of  rock  powder  in  acid  will 
leave  behind  all  insoluble  residue,  which  can  be  examined 
by  the  lens.  The  two  oxides  of  iron  can  be  detected  in  a 
similar  way  by  the  use  of  HCi  and  cyanide  salts  of  potash. 
This  list  can  be  further  extended ;  but  it  is  sufficient  to  say 
that  the  expert  in  qualitative  analysis  can  devise  similar  tests 
on  slides  that  will  give  under  the  lens  a  good  idea  of  the 
composition  of  the  rock  in  case  it  be  non-crystalline  or  com- 
pact. Boricky  suggests  the  action  of  pure  hydrofluosilicic 
acid  on  silicates  in  minute  fragments,  as  follows :  fix  a  minute 
particle  on  a  glass  plate  with  balsam  and  moisten  with  a  drop 
of  acid ;  place  under  a  bell  glass  near  a  vessel  with  water 
and  stand  for  twenty-four  hours ;  then  dry  by  placing  over 
calcium  chloride,  and  examine  with  a  lens,  when  fluosilicate 


PRELIMINARY  DESCRIPTION.  13 

of  potassium  will  show  as  cubes ;  of  sodium  as  hexagonal 
prisms.  Nepheline  compounds  when  powdered  and  touched 
with  HC1  will,  on  drying,  show  chloride  of  sodium  crystals. 
Klemert  and  Renard's  work  on  microchemistry  (Brussels, 
1886)  covers  the  subject  fully.  It  is  needless  to  add  that  the 
.blowpipe  set  should  always  be  on  hand  for  mineral  analysis. 
In  studying  the  shape  of  an  "  aureola  "  of  contact  meta- 
morphism  in  the  field,  it  may  be  well  to  bear  in  mind  that 
heat  transmission  in  slate  and  ordinary  shales  is  four  times  as 
rapid  with  the  bedding  planes  as  across  them.  We  can  find 
the  values  of  heat  transmission  in  any  rock  in  the  laboratory 
by  covering  with  wax  one  side  of  moderately  thin  sections, 
made  at  various  angles  with  the  bedding-planes,  or  along 
sections  where  the  rock  seems  to  show  variations  in  struc- 
ture or  density,  and  drilling  through  the  middle  of  each  a 
hole  of  sufficient  size  to  pass  a  platinum  wire,  which  will  be 
heated  by  an  electric  current.  The  heat  will  be  transmitted 
more  rapidly  in  a  thin  than  a  thick  section  with  a  given  size 
-of  wire,  and  the  relative  rates  of  transmsision  will  be  marked 
by  the  shape  of  the  melting  wax.  If  the  platinum  wire  be  no 
longer  than  the  thickness  of  the  section,  there  will  be  no 
heating  of  the  wax  by  radiation.  The  record  can  be  kept  by 
photographing  the  specimen,  or  dusting  upon  the  melted 
wax  a  powder  of  a  different  color.  A  series  made  at  vary- 
ing angles  will  give  the  heat  values  for  that  rock,  and  their 
comparison  with  similar  ones  of  the  same  species  from  an- 
other locality  may  show  differences  due  to  moisture,  density, 
•etc.,  as  heat  travels  faster  in  wet  than  in  dry  rocks  :  in  dense 
than  in  loose. 


ROCK-FORMING  MINERALS. 

Minerals  can  be  divided  into  two  classes :  those  which 
are  the  most  abundant,  arid  those  which  are  the  most  com- 
mon. The  most  abundant  minerals  are  generally  grouped 
in  a  few  species ;  the  most  common  minerals  may  never  be 
visible  to  the  eye  in  the  majority  of  cases ;  may  exist  always 
in  a  minute  proportion,  and  yet  be  always  present.  Under 
the  modern  theory  of  crystallization  from  a  perfectly  fluid 
magma  in  the  hot  abysses  of  the  earth's  crust  it  is  decided 
that  the  most  basic  combinations  are  first  to  form,  so  that 
they  are  frequently  included  within  those  forming  later.  If 
we  take  into  consideration  the  minerals  of  common  occur- 
rence, as  iar  as  that  term  stands  for  generality  of  occurrence, 
we  shall  find  that  our  list  contains  species  not  readily  seen 
with  the  eye  or  lens,  as  magnetite,  titanite,  specular  hematite, 
apatite,  allanite,  zircon,  and  olivine.  These  are  among  the 
first  to  form  in  the  fluid  magmas.  If  we  arrange  the  min- 
erals in  the  order  of  their  prominence  as  rock-formers,  we 
shall  find  that  the  ( M)  species  of  common  occurrence  are 
quartz,  feldspars,  micas,  amphiboles,  pyroxenes,  calcite,  and 
dolomite  ;  those  of  frequent  occurrence,  nepheline,  leucite, 
melilite,  sodalite,  haiiyne,  olivine,  chlorite,  talc,  serpentine, 
hydromicas,  garnet,  apatite,  epidote,  magnetite,  ilmenite, 
zircon,  and  tourmaline  ;  those  occurring  as  rocks  of  large 
extent,  by  themselves,  calcite,  dolomite,  magnesite,  cryolite, 
asphalt,  coal,  iron  ores,  salt,  bauxite,  sulphur,  and  a  few 
sulphides. 

14 


ROCK-FORMING   MINERALS.  1 5 

I.  Quartz.     Rhombohedral.     It  occurs  (i)  phenocrystal- 
line  : 

(a)  As  an  independent  rock  in  veins,  beds,  and  masses  of 
primary  or  metamorphic  origin  ; 

(b)  As  a  necessary  component  in  many  primary  rocks,  and 
especially  in  the  metamorphic  schists,  e.g.,  granite,  gneiss. ; 

(c)  As  an  essential  element  in  many  rocks  to  form  species 
of  an  otherwise  quartzless   class,  as   quartz-basalt,  quartz- 
diorite  ;  and 

(d)  As  principal  ingredient  in  many  clastic  rocks  (sand- 
stones, conglomerates),  and  as  sand  and  gravel. 

It  occurs  (2)  cryptocrystalline  and  amorphous  : 

(a)  As  agate, which  is  a  variegated  combination  of  alternate 
layers   of   common  quartz  (amethyst,  or  chalcedony)  with 
jasper,  carnelian,  etc.,  formed  usually  in  the  amygdaloidal 
cavities  of  eruptive  rocks,  as  geodes,  or  in  metallic  veins. 
The  extensive  establishment  for  manufacturing  articles  from 
agate  at  Oberstein  long  since  exhausted  the  local  deposit, 
and  for  many  years  the  supply  has  come  from  the  volcanic 
rocks  of  Uruguay.     Agate  is  also  found  in  the  similar  rocks 
of  Iceland,  the  Faroe  Islands,  and  (from  the  decomposition  of 
the  rocks)  in  the  sands  of  Lake  Superior  and  the  northern 
part  of  the  Mississippi  River.     Moss  agates  are  not  banded. 

(b)  As  jasper  (bright  red),  flint  (grayish  blue  to  black  from 
carbon),  and   chert,  or  hornstone  (gray,  yellow,  green,  red, 
brown,  black).    Jasper  is  generally  associated  with  iron  ores, 
as  it  obtains  its  color  from   anhydrous  sesquioxide  of  iron, 
and  can  be  traced  by  regular  gradations  from  a  slightly  fer- 
rated  cryptocrystalline  form  of  quartz  to  a  slightly  siliceous 
hematite,  as  the  ferric  solutions  have  more  and  more  re- 
placed silica  by  metachemism.     It  occurs  under  the  same 
conditions  as  hornstone,  as  concretions  and  layers  in  rocks. 
Flint  occurs  as  concretions  in  calcareous  sediments,  which, 
in  some  cases,  have  been  formed  from  the  spiculas  of  sih- 


l6  MANUAL    OF  LITHOLOGY. 

ceous  sponges.  The  principal  locations  are  the  Chalk  of 
northern  Europe,  and  the  Upper  Jurassic  of  Bavaria. 
Hornstone  is  not  so  tough  as  flint,  and  breaks  with  a  more 
splintery  fracture.  It  is  abundant  in  the  Siluro-Cambrian 
limestone  of  the  eastern  part  of  Pennsylvania,  and  is  the 
form  of  quartz  frequently  met  with  in  petrified  wood. 
Basanite  is  a  black  jasper. 

H.  7 ;  Gr.  2.5-2.8,  average  2.6.  Colorless  and  limpid,  or 
variously  colored.  Comp.  SiO,.  Luster  vitreous,  sometimes 
resinous  or  waxy,  especially  on  the  surface  of  fractures. 

Bp.  Crystalline  variety :  alone,  unaltered ;  with  soda  dis- 
solves with  effervescence ;  untouched  by  microcosmic  salt ; 
cryptocrystalline  variety :  with  borax  dissolves  to  a  clear 
glass.  Chem.  Crystalline  :  soluble  in  HF  alone  ;  cryptocrys- 
talline :  slightly  acted  upon  by  caustic  alkali. 

Weathering.  Crystalline :  unchanged,  though  crystals 
have  been  found  with  corroded  edges  ;  cryptocrystalline : 
forms  a  white  crust,  as  in  flints. 

Associated  with  almost  every  other  mineral  except 
ieucite,  nepheline,  and  melilite  ;  but  it  is  more  commonly 
found  with  orthoclase  and  the  acid  silicates.  It  frequently 
occurs  with  tourmaline,  rutile,  cassiterite,  and  topaz.  It  is 
found  more  frequently  with  hornblende  than  pyroxene,  with 
muscovite  than  biotite,  and  seldom  with  olivine. 

2.  Tridymite.  Hexagonal.  Tabular  crystals,  grains. 
H.  7  ;  Gr.  2.28-2.33.  Colorless.  Luster  of  fracture,  vitreous  ; 
of  face,  pearly.  Fracture  conchoidal.  Comp.  SiO2. 

Bp.  Infusible ;  with  soda  fuses  with  effervescence  to  a 
colorless  glass.  Chem.  Pure  silica,  soluble  in  a  boiling 
solution  of  sodium  carbonate. 

Weathering.    Gradually  changes  from  colorless  to  white. 

Tridymite  occurs  generally  in  acid  extrusive  rocks  in 
thin  minute  glassy  hexagonal  crystals.  It  has  been  found  in 
the  massive  states  of  these  rocks  and  in  volcanic  ash  ;  also 


ROCK-FORMING   MINERALS.  I/ 

as  enclosures  in  opal  and  quartz.  It  is  a  frequent  com- 
ponent of  rhyolites,  andesites,  and  trachytes. 

3.  Opal.     Massive,  amorphous. 

H.  5.5-6.5  ;  Gr.  1.9-2.3.  Variously  colored,  colorless,  or 
characterized  by  a  rich  play  of  colors  that  is  termed  "  opal- 
escent." Transparent  to  opaque.  Luster  usually  waxy  or 
greasy,  sometimes  resinous  and  vitreous. 

Bp.  Most  varieties  decrepitate  on  heating,  and  yield 
water  in  the  matrass ;  infusible;  become  opaque,  except  the 
yellowish  varieties,  which  contain  hydrated  sesquioxide  of 
iron  and  turn  red  ;  there  is  no  change  of  color.  Chem. 
Amorphous  silica  combined  with  non,essential  water,  which 
may  vary  from  2-20  per  cent,  but  usually  varies  from  3-9, 
and  a  small  amount  of  coloring  matter.  It  differs  from 
quartz  in  being  soluble  in  a  solution  of  caustic  potash, 
from  which  it  can  be  precipitated  by  sufficient  ammonium 
chloride,  and  in  being  more  soluble  in  heated  alkaline 
waters. 

Weathering.  Forms  a  colorless  crust  on  the  earthy  and 
porous  solid  forms  which  are  colored.  Is  dissolved  by  alka- 
line waters  and  disappears  when  in  the  form  of  ooze. 

Opal  occurs  (i)  as  metachemic  exfiltrations  in  eruptive 
rocks,  (a),  as  precious  opal,  which  fills  vesicular  cavities  or 
clefts  in  trachytic  rocks,  as  in  Hungary  and  Mexico,  and 
sometimes  in  basalt ;  (£),  as  hyalite,  a  transparent  and  color- 
less form  which  is  found  under  similar  conditions  in  basaltic 
rocks,  and  with  a  globular,  reniform,  botryoidal,  or  stalac- 
titic  structure. 

It  occurs  (2)  in  metamorphic  rocks,  as  in  some  slates  and 
crystalline  rocks.  The  "  Guinea  quartz "  of  the  rocks 
associated  with  the  iron  ores  of  central  Virginia  is  said  to 
be  opal. 

It  occurs  (3)  in  petrifactions  where  the  cellulose  of  wood 
has  been  replaced  by  this  soluble  silica. 


18  MANUAL    OF  LITHOLOGY. 

It  occurs  (4)  from  the  decomposition  of  siliceous  minerals 
of  volcanic  rocks  to  form  fiorite,  which  is  similar  to  hyalite. 

It  occurs  (5)  in  concretionary  deposits  about  the  Iceland 
and  Yellowstone  geysers  under  the  name  of  geyserite.  This 
is  soft  when  first  formed,  but  hardens  on  exposure ;  color 
white  or  grayish  ;  stalactitic,  massive  (compact  and  scaly), 
usually  opaque,  sometimes  crumbly  on  drying. 

It  occurs  (6)  in  organic  aggregates,  as  the  skeletons  of 
hexactinellid  sponges  ;  the  shells  of  radiolarians  and  diatoms, 
to  form  tripoli  or  randanite  and  through  the  agency  of  con- 
fervid  algas  to  form  geyserite. 

THE   FELDSPARS. 

After  quartz  this  series  is  the  most  important  of  rock- 
formers,  and  especially  in  eruptives,  of  which  the  larger 
proportion  is  a  feldspar.  Crystallographically  it  is  divided 
into  two  groups,  the  monoclinic,  or  (from  the  principal  type) 
the  orthoclases,  and  triclinic,  which  is  further  divided  into  the 
anorthoclases  and  the  plagioclases. 

In  the  orthoclases  the  angle  measured  over  the  two  most 
perfect  cleavage  planes  is  90°  ;  in  the  anorthoclases  it  is 
slightly,  and  in  the  plagioclases  considerably,  less  than  that 
angle.  All  feldspars  tend  to  form  twins,  and  in  some  cases 
the  duplication  is  marked. 

THE   ORTHOCLASES. 

These  are  orthoclase  and  sanidine.  The  former  occurs 
usually  in  the  rocks  of  the  Archaean  and  in  the  intrusives, 
the  latter  in  the  extrusives.  Orthoclase  even  when  fresh 
never  has  the  glassy  habit  of  sanidine,  and  approaches  it 
most  nearly  in  orthophyric  porphyries. 

4.  Orthoclase  (Potash  Feldspar).     Monoclinic. 

H.  6 ;  G.  2.5-2.56.  Transparent-translucent.  Colorless, 
more  frequently  greenish  white  or  flesh-red.  Luster  vitreous, 
sometimes  pearly  on  cleavages.  Comp.  KAlSi3O8. 


ROCK-FORMING   MINERALS.  19 

Bp.  Fus.  5  on  thin  edges  to  a  dull  porous  glass  ;  with 
microcosmic  salt,  soluble  with  difficulty,  leaving  a  skeleton 
of  silica  ;  with  cobalt,  fused  edges  are  colored  blue.  Chem, 
Untouched  by  acids,  except  HF,  which  completely  decom- 
poses it ;  decomposed  by  fusion  with  alkaline  carbonates. 

Weathering.  Decomposes  with  comparative  rapidity  by 
removal  of  the  alkali,  and  changes  to  kaolin  more  readily  than 
albite  ;  but  less  so  than  labradorite,  anorthite,  and  oligoclase, 

It  is  always  more  or  less  crystal  in  porphyries  and  por- 
phyritic  schists.  In  massives  it  loses  its  crystal  form  with 
the  increasing  granularity  of  the  mass,  and  never  holds  it  in 
non-porphyritic  schists.  The  crystals  are  frequently  broken 
in  massives  from  movement  of  the  magma,  and  in  schists 
from  orogenic  movements ;  but  in  the  latter  case  the  edges 
alone  suffer.  It  twins  most  commonly  after  the  Carlsbad 
law,  less  commonly  after  that  of  Baveno,  least  so  after  that 
of  Manebach.  It  can  be  separated  from  the  lime-soda  feld- 
spars by  classification  and  sorting  when  the  classification 
ratio  is  small.  It  can,  further,  be  distinguished  from  them 
by  the  absence  of  striations,  which  generally  exist  in  the 
plagioclases  from  their  peculiar  (albitic)  twinning  ;  but  the 
flesh-red  variety  (or  rather  mixture)  perthite,  from  Perth 
(Upper  Canada),  Egypt,  etc.,  shows  what  seem  to  be  stri- 
ations, from  the  intercrystallization  of  parallel  laminae  of 
orthoclase  and  albite.  Orthoclase  in  quartzose  eruptives  is 
associated  with  hornblende  rather  than  pyroxene.  Potash 
feldspar  and  potash  mica  are  commonly  associated.  In  the 
older  eruptives  it  occurs  with  nepheline  more  frequently 
than  do  the  plagioclases. 

5.  Sanidine  (Potash-soda  Feldspar).  Monoclinic.  Tab- 
ular crystals,  grains. 

It  behaves  like  orthoclase  with  the  exception  of  showing 
more  soda.  Luster  vitreous.  Color  grayish,  yellowish  white. 

It   occurs   in   extrusive    rocks,   as    phonolite,   trachyte, 


2O  MANUAL    OF  LITHOLOGY. 

pitchstone,  etc. ;  has  a  fissured  appearance  due  to  the  flow 
subsequent  to  crystallization ;  is  found  with  quartz,  plagio- 
clase,  nepheline,  leucite,  haiiyne,  and  the  black  bisilicates. 

THE   ANORTHOCLASES   (Parorthodases,  Zirkel). 

These  are  all  triclinic,  but  with  slight  deviation  from  a 
monoclinic  habit,  and  their  cleavage  angle  differs  so  little 
from  that  of  orthoclase  that  they  cannot  be  placed  with  the 
plagioclases.  Some  authorities  hold  that  they  are  ortho- 
clases  deformed  by  slight  pressure ;  as  orthoclase  under 
pressure  assumes  the  microstructure  of  microcline,  and  the 
others  of  the  group  are  monoclinic  on  heating.  Zirkel 
rightly  objects  to  the  prefix  an-,  as  it  indicates  a  divergence, 
not  a  great  similarity,  and  suggests  par  orthoclase. 

6.  Microcline  (Potash  Feldspar.)  Triclinic.  Never  in 
perfectly  bounded  crystals ;  usually  in  irregular  grains ; 
twinned  to  form  polysynthetic  masses  with  both  albite  and 
pericline,  which  (masses)  twin  according  to  the  three  laws 
as  with  orthoclase. 

H.  6-6.5  5  Gr.  2.54-2.57.  Fracture  uneven.  Brittle. 
Luster  vitreous,  sometimes  pearly.  Color  white  to  yellowish, 
red,  green ;  by  transmitted  light  colorless.  Transparent- 
translucent.  Comp.  KAlSi3O8,  like  orthoclase,  but  carrying 
soda  up  to  5$,  and  lime  to  \%.  Bp.  and  chem.  like  orthoclase. 

Microcline  can  only  be  safely  distinguished  from  ortho- 
clase by  the  microscope,  as  it  occurs  with  it,  and  under 
similar  conditions,  so  that  it  frequently  replaces  it.  It  is 
generally  the  feldspar  in  graphic  granite  (pegmatite) ;  is 
common  to  granites,  gneisses,  syenites,  and  elaeolite-syenites  ; 
less  common  in  porphyries,  and  then  only  in  the  intratelluric 
crystals ;  almost  wanting  in  the  groundmass.  It  does  not 
replace  sanidine  in  the  extrusives.  Some  authorities  doubt 
the  alteration  of  orthoclase  to  microcline  by  pressure,  as  it 
is  found  in  cavities  in  rocks. 


ROCK-FORMING   MINERALS.  21 

7    and    8.    Anorthoclase    and    Cryptoperthite.      Two 

species  have  thus  far  been  agreed  upon  in  the  potash-soda 
mixtures,  and  a  variety  of  names  have  been  given  them. 
Following  Brogger,  they  are  a  potash-soda  variety,  cryptoper- 
thite,  and  a  soda-potash  variety,  microperthite  (anorthoclase  of 
Rosenbusch,  parorthoclase  of  Zirkel).  They  are  usually  (m), 
though  Fouque"  reports  anorthoclase  crystals  from  Fayal 
5  mm.  long  and  2  mm.  thick. 

Cryptoperthite  (potash-soda  variety)  is  assumed  to  be  an 
interlamination  of  plates  of  orthoclase  (or  microcline)  and 
albite  of  such  minuteness  as  to  be  invisible  under  the 
microscope,  and  to  act  as  a  homogeneous  body.  The 
characteristics  are  similar  to  those  of  microcline.  Anortho- 
clase (soda-potash  variety),  according  to  Fouqu£,  has  Gr. 
2.547-2.620 — the  heavier  specimen  coming  from  an  olivine- 
andesite.  The  average  is  2.580,  that  of  microcline  being 
2.560.  They  twin  polysynthetically,  and  the  mass  thus 
formed  twins  according  to  the  three  laws  as  with  orthoclase. 
They  are  found  in  augite-  and  hornblende-andesites,  augite- 
syenites,  trachytes,  rhyolites,  and  peculiar  rocks  of  the 
island  of  Pantelleria  called  pantellerites. 

THE   PLAGIOCLASES. 

The  members  of  this  group  occur  crystal,  granular, 
and  cryptocrystalline  to  compact.  They  are  mixtures  of  a 
typical  albite  (L)  and  anorthite  (N),  as  follows : 

L=NaAlSisO8 
N=CaAl2Si,08 

Cleavage  Angle. 

Albite  varies  from  L,N0  to  L8Nt 86°  24' 

Oligoclase         "      I^N,  "   I^N, 86°  08' 

Andesine  "      L3N,  "   L.N, 86°  14' 

Labradorite       "      LtN,  "   L,N2 86°  04' 

Anorthite  "      LtN.  "  L.N, 85°  50' 


MANUAL    OF  L1THOLOGY. 

On  a  fresh  fracture,  when  the  light  falls  somewhat  ob- 
liquely on  the  basal  (cleavage)  plane,  a  striation  generally 
.appears,  which  is  due  to  polysynthetic  twinning  of  thin 
laminas.  While  this  is  an  indication  of  the  group,  its 
absence  is  not  an  indication  of  another  group,  as  it  is  not 
quite  universal.  The  crystals  are  never  so  large  as  the 
large  orthoclases ;  but  they  show  the  same  fractures.  The 
microscope  has  shown  that  Breithaupt's  laws  of  paragenesis 
are  not  universal ;  yet  it  can  be  noted  that,  as  far  as  the  un- 
aided eye  is  concerned,  the  more  acid  plagioclases  are  the 
more  usually  found  with  orthoclase  and  quartz  ;  while  the 
more  basic,  as  labradorite  and  anorthite,  are  generally  absent 
under  similar  circumstances.  The  decomposition  of  rocks 
and  resulting  metachemic  formation  of  secondary  minerals 
frequently  allows  a  determination  of  the  ingredients  of  com- 
pact eruptives  with  a  high  degree  of  certainty,  as  shown  by 
the  microscope,  or  by  following  the  ,mass  to  its  centre 
where  the  crystals  are  large  enough  to  be  readily  recog- 
nized. In  some  cases  the  materials  for  the  secondary 
minerals  have  been  leached  from  the  country  rock  of  the  in- 
jected eruptive,  and  some  authorities  would  extend  this  to 
all  cases ;  but  the  fact  that  certain  secondary  minerals  seem 
to  favor  rocks  of  definite  mineralogical  and  chemical  com- 
position points  to  an  origin  within  the  rock.  It  is  generally 
the  case  that  an  abundance  of  calcite  or  calcareous  zeolites 
(chabazite,  phillipsite,  stilbite,  etc.),  in  a  compact  basic  erup- 
tive enclosed  in  non-calcareous  walls,  is  due  to  the  decom- 
position of  the  minerals  in  the  rock  itself,  and  generally 
indicates  the  presence  of  a  lime  feldspar. 

Association  will  frequently  enable  us  to  detect  an  obscure 
Jorm  of  this  group,  as  we  find  together  frequently  orthoclase 
.-and  oligoclase,  or  orthoclase,  oligoclase,  and  hornblende ; 
Jabradorite  and  pyroxene  or  hypersthene  ;  while  we  less 
seldom  find  together  labradorite  or  anorthite  and  quartz, 


ROCK-FORMING   MINERALS.  2$ 

•or  orthoclase  and  leucite,  oligoclase  and  leucite  or  nephe- 
line,  etc.  According  to  rapidity  of  weathering,  the  feld- 
spars can  be  arranged  in  the  following  order,  beginning 
with  the  most  readily  decomposed  :  labradorite,  oligoclase, 
•orthoclase,  albite.  If  there  be  two  feldspars  in  a  rock  and 
one  be  weathered,  it  may  be  possible  to  determine  it  by  the 
unweathered  one,  from  the  general  habit  of  association,  to- 
gether with  the  density  of  the  rock. 

9.  Albite  (Soda  Feldspar). 

H.  6-6.5  ;  Gr.  2.62-2.65.  Luster  pearly  on  cleavages, 
otherwise  vitreous.  Color  generally  white,  sometimes 
bluish,  gray,  reddish,  greenish,  green,  but  colorless  by 
transmitted  light  when  thin,  as  is  the  case  of  all  the  group. 
Transparent-subtranslucent.  Fracture  uneven.  Brittle. 

Bp.  Fus.  at  4  to  a  colorless  glass  and  gives  a  strong 
flame  reaction  for  Na.  Chem.  Untouched  by  acids. 

It  is  found  in  granites  and  gneisses  and  the  crystalline 
-schists ;  in  contact  zones  of  diabase  ;  in  trachytes,  andesites, 
phonolites,  granular  limestones,  etc.  Untwinned  crystals  are 
rare.  Not  weathered  easily. 

10.  Oligoclase  (Soda-lime  Feldspar). 

H.  6-7  ;  Gr.  2.65-2.67.  Luster  vitreo-pearly  or  waxy  to 
vitreous.  Color  usually  white  tinged  with  shades  of  grayish 
green,  gray,  green,  and  red.  Transparent-subtranslucent. 
Fracture  conchoidal,  uneven. 

Bp.  Fus.  3.5  to  clear  enamel-like  glass.  Chem.  Scarcely 
affected  by  acids. 

It  is  necessary  in  diorite,  trachyte,  and  andesite  ;  is  found 
with  orthoclase  in  granite  and  syenite ;  is  seldom  found  with 
leucite  and  nepheline.  Occurs  in  massive  grains  and  crys- 
tals, and  twins  according  to  the  Carlsbad,  albite,  and  peri- 
<:line  laws. 

Weathers  more  readily  than  orthoclase  and  albite  to 
kaolin  and  light-colored  mica. 


24  MANUAL   OF  LITHOLOGY. 

11.  Andesine  (Soda-lime  Feldspar). 

H.  5-6;  Gr.  2.68-2.69.  Color  and  luster  similar  to 
oligoclase. 

Bp.  Fus.  5  on  thin  splinters  ;  with  borax  forms  a  clear 
glass.  Chem.  Soluble  in  HF;  partially  in  the  other  acids. 
It  occurs  similarly  to  oligoclase  in  the  eruptives  and 
gneisses;  weathers  easily  to  kaolin,  and  twins  like 
oligoclase. 

12.  Labradorite  (Lime-soda  Feldspar).     Rarely  crystal ; 
lath-shaped  ;  generally  massive-granular;  sometimes  crypto- 
crystalline. 

H.  6:  Gr.  2.70-2.72.  Luster  pearly  on  basal  cleavage; 
otherwise  vitreous-subresinous.  Color  gray,  brown,  green- 
ish,  rarely  white.  Usually  a  play  of  colors  on  cleavage 
faces.  Translucent-subtranslucent. 

Bp.  Fus.  3  to  colorless  glass.  Chem.  When  fresh  is 
with  difficulty  soluble  in  HC1,  and  leaves  residue ;  when 
powdered  is  easily  soluble  in  hot  HC1. 

Weathers  like  anorthite.  It  is  confined  to  the  basic 
eruptives  and  schists,  is  necessary  to  basalt  and  dolerite, 
abundantly  developed  in  the  Archaean  rocks  of  Canada,  and 
occurs  chiefly  in  quartzless  rocks,  and  seldom  in  those  carry- 
ing nepheline  and  leucite. 

13.  Anorthite  (Lime  Feldspar).     Generally  non-crystal, 
and  in  lath-shaped,  granular,  and  spathic  forms. 

H.  6-7  ;  Gr.  2.66-2.78.  Luster  somewhat  like  labradorite. 
Color  white,  grayish,  reddish.  Transparent-translucent. 
Fracture  conchoidal.  Brittle. 

Bp.  Fus.  4.5-5  to  colorless  glass.  Chem.  Decomposed 
by  HC1  with  separation  of  gelatinous  silica. 

It  is  found  in  a  few  diorites  (corsite) ;  in  diabase,  gabbro, 
norite,  and  basic  schists  that  have  probably  been  metamor- 
phosed from  gabbros.  In  Vesuvian  lavas  it  occurs  in  greasy 


ROCK-FORMING   MINERALS.  2$ 

crystals  when  in  the  mass,  but  in  limpid  and  vitreous  ones 
when  in  druses.     It  weathers  easily. 

THE    MICAS. 

The  members  of  this  group  are  monoclinic,  but  are 
peculiar  in  having  a  hexagonal  or  orthorhombic  habit  in 
their  crystals  and  physical  characteristics.  They  generally 
form  folia  in  rocks  with  exact  hexagonal  outline  when 
crystal,  and  frequently  they  have  considerable  thickness ; 
but  the  usual  habit  is  the  basal  plane  with  irregular 
boundaries.  These  folia  can  be  distinguished  from  those 
of  the  chlorite  group  by  their  elasticity,  the  latter  being 
perfectly  flexible,  and  the  elasticity  increases  with  the 
acidity  of  the  mica,  while  brittleness  increases  with  the 
basicity.  They  can  thus  be  arranged,  according  to  amount 
of  silica,  lepidomelane  (laminae  brittle  and  little  elastic), 
biotite,  phlogopite,  lepidolite,  muscovite,  the  last  being  very 
tough  and  elastic.  Frequently  the  mica  will  be  a  mixture 
of  muscovite  and  biotite,  and  always  following  the  law  that 
the  muscovite  is  external,  whether  as  the  rim  of  a  single 
plate  or  as  the  outside  plates  of  a  crystal  series.  This 
mixture  cannot  be  detected  by  the  eye,  and  only  chemically 
when  the  mass  is  large. 

The  Acid  Micas. 

14.  Muscovite  (Potash  Mica). 

H.  2-2.5  ;  Gr.  2.83-2.9.  Luster  vitreous-pearly.  Thin 
laminae  flexible  and  elastic.  Color  white,  gray,  brown,  green, 
yellow,  violet,  rarely  red ;  by  transmitted  light,  light 
shades  of  yellow  and  green.  Transparent-translucent. 
Comp.  H2KAl3Si3O12. 

Bp.  In  closed  tube  gives  water  that  frequently  reacts 
for  fluorine  ;  whitens  and  fus.  5.7  to  a  gray  or  yellow  glass  ; 
with  fluxes  reacts  for  iron ;  sometimes  Mn,  rarely  Cr ; 


26  MANUAL    OF  LITHOLOGY. 

decomposed  by  fusion  with  alkaline  carbonates.  Chemt 
Slightly  attacked  by  acids. 

It  is  an  essential  in  granite  and  gneiss,  and  is  found  in  a 
few  quartz-porphyries;  never  in  eruptives  other  than  above 
given.  We  find  muscovite  associated  with  quartz  and  potash 
feldspar  in  granitoid  rocks.  It  is  not  commonly  found  in 
porphyries. 

Weathers  to  steatite  and  serpentine,  and  is  itself  an  alter- 
ation product  of  other  minerals.  Among  its  varieties  are : 

I4a.  Damourite  (Hydromica). 

A  variety  of  muscovite  that  is  extended  to  include 
(Dana)  most  hydromicas,  margarodite,  sericite,  etc.  They 
may  give  off  more  water  in  the  closed  tube  than  does 
muscovite  ;  but  they  do  not  contain  any  more  chemically 
combined.  Folia  less  elastic.  Luster  pearly  or  silky.  Feel 
like  talc  (formerly  much  hydromica  schist  was  called  talc- 
schist  until  distinguished  by  Dewey).  Its  difference  is  shown 
by  the  action  of  the  two  with  cobalt  solution  and  HF. 

I4b.  Agalmatolite  (Pagoda  Stone).  Compact,  amor- 
phous. 

Luster  feeble,  waxy.  Color  grayish,  greenish,  yellowish. 
Like  a  compact  muscovite,  and  produced  from  the  altera- 
tion of  iolite,  spodumene,  scapolite,  and  similar  minerals. 
The  Chinese  variety  has  H.  2-2.5  ;  Gr.  2.78-2.81.  Part  of 
the  Chinese  agalmatolite  is  pinite,  which  is  a  similar  altera- 
tion product,  but  with  less  silica;  part  is  compact  pyro- 
phyllite,  and  part  is  steatite.  It  is  used  for  carving  miniature 
images,  etc. 

15.  Paragonite  (Soda  Mica). 

H.  2.5-3  5  Gr.  2.78-2.90.  Luster  pearly.  Color  yellowish, 
grayish,  greenish  ;  colorless  by  transmitted  light.  Translu- 
cent, and  smaller  scales  transparent.  Comp.  HaNaAl3Si3O12. 

Bp.  Fusible  with  difficulty;  some  varieties  whiten  on  edges 
and  exfoliate.  Occurs  in  crystalline  schists  and  phyllites, 


ROCK-FORMING   MINERALS.  2? 

in   irregularly  bounded   plates  and    fine    scaly    aggregates 
looking  like  talc  ;  never  in  massives. 

16.  Lepidolite  (Lithia  Mica).     Commonly  massive,  scaly, 
.granular. 

H.  2.5-4;  Gr.  2.8-2.9.  Luster  pearly.  Color  peach- 
blow  red,  rose-red,  violet  gray,  yellowish,  greenish, 
white  ;  colorless  by  transmitted  light.  Translucent.  Comp. 
Al(SiO4)3Al2KLiH  +  Al(Si30B)3K3Li3(AlF2)3. 

Bp.  In  closed  tube  gives  water  and  reaction  for  F. 
Fus.  2-2.5  with  intumescence  to  a  whitish  .or  grayish  glass, 
and  sometimes  gives  the  lithia-flame  reaction ;  with  fluxes 
&ome  varieties  react  for  Fe  and  Mn.  Chem.  Only  partially 
decomposed  by  acids  before  fusion  ;  after,  it  gelatinizes  with 
HC1.  Occurs  in  granite,  gneiss,  and  pegmatitic  secretions 
from  them. 

17.  Zinnwaldite,  Lithionite  (Lithia-iron  Mica). 

H.  2.5-3  »  GT.  2.82-3.21.  Luster  often  pearly.  Color  like 
lepidolite  with  brown  shades  and  darker  gray  ;  by  trans- 
mitted light  dark  brown  to  light  yellow  and  grayish  white. 
Fine  wrinkling  on  cleavage  plane  from  twinning. 

Bp.  Similar  to  lepidolite,  but  fuses  more  easily  and 
:gives  F  reaction.  Comp.  (K,Li)3FeAl3Si6O16(OH,F).  Occurs 
in  tin-bearing  granites  in  Germany,  France,  Cornwall,  etc., 
.and  in  pegmatitic  secretions  in  granite  and  gneiss  ;  necessary 
in  greisen. 

18.  Biotite  (Magnesia-iron  Mica). 

H.  2.3-3  ;  Gr.  2.7-3.1.  Luster  splendent-pearly  on  cleav- 
ages, black  kinds  submetallic ;  lateral  surfaces  vitreous. 
Color  green-black ;  deep  black  in  thick  crystals ;  by  trans- 
mitted light  brown  in  Archaean  rocks;  frequently  green 
with  hornblende  of  similar  color,  but  not  in  massive  por- 
phyries, and  rare  in  granites.  Transparent-opaque.  Comp. 

<HK).(Mg,Fe).(Al,Fe),SiAr 

Bp.  Water  in  closed  tube  ;  in  open  tube  reaction  for  F 


28  MANUAL    OF  LITHOLOGY. 

and  for  Fe  ;  with  fluxes  varies  greatly  in  different  varieties ; 
whitens  on  thin  edges  and  fuses.  Chem.  Completely 
decomp.  by  H,SO4  with  separation  of  silica  in  thin  scales. 

Occurs  in  massives  and  Archaean  rocks — not  in  crystals, 
but  as  flakes  and  plates  with  irregular  boundaries.  In 
granites  it  is  intergrown  with  muscovite,  as  has  been 
described  on  p.  25.  It  is  one  of  the  first  generations  in 
porphyritic  rocks,  and  is  generally  absent  from  the  second 
generations  in  the  groundmass ;  is  one  of  the  most  common 
results  of  contact  metamorphism,  and  is  often  an  alteration 
product  of  chlorite.  It  is  more  abundant  in  acid  than  basic 
rocks. 

(a)  Rubellan  is  an  altered  ferruginous  biotite  found  in 
some  basalts. 

19.  Phlogopite  (Magnesia  Mica).    In  crystals  and  plates. 
H.  2.5-3 ;  Gr.  2.78-2.85.     Thin   laminae   are   tough   and 

elastic.  Luster  pearly,  often  submetallic  on  cleavages.  Color 
yellowish  brown,  brownish  red  with  copper-like  reflections; 
also  pale  brownish  yellow,  green,  white,  colorless.  A  small 
candle  flame  viewed  through  thin  plates  shows  commonly  a 
six-rayed  star  due  to  acicular  inclusions.  Transparent-trans- 
lucent. Comp.  H6K2Mg7Ala(SiO4)7,  so  that  it  may  be  called 
a  biotite  lacking  iron. 

Bp.  In  closed  tube  gives  little  water;  frequently  in  open 
tube  a  small  amount  of  F;  with  fluxes  little  or  no  iron; 
whitens  and  fuses  on  thin  edges.  Chem.  Like  biotite ;  alters 
to  talc.  Occurs  mostly  in  Archaean  granular  limestone  ;  also 
in  serpentine. 

20.  Lepidomelane  (Iron-magnesia  Mica).     Tabular,  mas- 
sive. 

H.  3  ;  Gr.  3-3.2.  Luster  adamantine-vitreous  or  pearly. 
Color  black  with  greenish  reflection.  Streak  grayish  green. 
Translucent  in  thin  laminae,  otherwise  opaque.  Somewhat 


ROCK-FORMING   MINERALS.  29 

brittle.     Comp.   (H,K)aFe3(Fe,Al)4(SiO4)6.     This  is   a  ferric 
biotite. 

Bp.  At  red  heat  turns  brown  and  fuses  to  a  black  mag- 
netic globule.  Chem.  Most  easily  of  all  micas  decomposed 
by  acids,  and  by  HC1  readily  with  separation  of  silica  scales. 
Occurs  more  restrictedly  than  biotite  in  granite,  etc. 

Brittle  Micas. 

21.  Margarite  (Pearl  Mica).     Tabular,  scaly,  massive. 

H.  3.5-4.5  ;  Gr.  2.99-3.08.  Brittle.  Luster  of  base  pearly. 
Color  grayish,  reddish,  yellowish,  white.  Transparent-sub- 
translucent.  Comp.  H2CaAl4Si2O13. 

Bp.  Water  in  closed  tube ;  whitens  and  fuses  on  edges. 
Chem.  Slowly  and  imperfectly  decomposed  by  boiling 
H2SO4.  Commonly  associated  with  corundum  in  contact 
formations. 

(a)  Ottrelite  and  phyllite  belong  here,  and  are  found  only 
in  crystalline  schists. 

CHLORITES. 

The  color  of  these  green  minerals  is  due  to  ferrous  iron 
and  gives  them  their  name.  They  are  sometimes  red  or 
brown  ;  of  low  hardness  and  with  flexible  laminas  —  tough 
and  not  elastic.  They  are  all  monoclinic  in  habit,  though 
they  simulate  hexagonal  shapes,  as  the  angles  about  the  basal 
plane  are  120°.  Chem.  the}'  are  (ferrous)  iron-magnesian 
silicates  of  aluminum  with  chemically  combined  water  and 
no  alkalies,  and  seem  to  be  altered  from  rich  iron-magnesia 
silicates  (hornblende,  pyroxene,  biotite,  phlogopite,  etc.). 
They  occur  generally  in  flat  or  bent  laminas,  and  are  at- 
tacked by  acids. 

22  Clinochlore  (Magnesia-iron  Chlorite).  Crystal,  coarse 
scaly,  granular,  earthy,  massive. 

H.  2-2.5  ;  Gr.  2.65-2.78.  Luster  pearly  on  cleavages. 
Color  deep  grass-green-olive  green,  pale  green-yellowish, 
white,  also  rose  and  red  (chromium  variety)  by  transmitted 


30  MANUAL    OF  LITHOLOGY. 

light    green   or   yellow-brown.      Transparent-translucent 
Comp.  H8Mg6AlaSi,018. 

Bp.  Gives  water ;  whitens  and  fuses  with  difficulty  on 
thin  edges  of  small  pieces  to  a  grayish-black  glass ;  with 
borax  reacts  for  Fe  (sometimes  Cr) ;  some  kinds  exfoliate. 
Chem.  Wholly  decomposed  by  H2SO4. 

23.  Penninite  (Magnesia-iron  Chlorite).    Flat  or  bent  lam* 
inae,  massive,  compact  cryptocrystalline. 

H.  same  as  22 ;   Gr.  2.6-2.85.     Luster,  etc.,  like  22. 

Bp.  Water  in  closed  tube ;  exfoliates  slightly  and  fuses 
with  difficulty ;  reacts  for  Fe  (and  Cr  in  many  cases).  Chem. 
Like  22,  and  also  partly  decomposed  by  HC1. 

24.  Prochlorite  (Iron-magnesia  Chlorite).     Massive,  fol- 
iated, granular. 

H.  i. -2.;  Gr.  2.78-2.96.  Luster  of  cleavages  feebly  pearly. 
Color  darker  shades  of  green ;  by  transmitted  light  green 
(sometimes  red).  Streak  more  generally  uncolored  than  that 
of  the  others.  Opaque-transparent  only  in  thin  folia.  Comp. 

H4(Mg,Fe)sSiA- 

Bp.  same  as  22. 

The  chlorites  are  most  widely  distributed  and  give  to 
many  eruptives  their  green  color.  They  also  occur  in  the 
basic  schists.  Prochlorite  occurs  most  frequently  in  erup- 
tives, the  other  two  in  the  schists.  The  cromium  varie- 
ties are  found  in  olivine-bearing  schists. 

THE   PYROXENES 

These  are  widely  distributed  eruptive  and  schistose 
rock-formers,  which  crystallize  in  orthorhombic,  mono-,  or 
triclinic  forms ;  but  agree  in  having  an  angle  of  87°  and  93° 
to  the  fundamental  prism,  and  a  more  or  less  distinct  cleav- 
age parallel  to  it. 

Orthorhombic  Section. 

25.  Enstatite.     Rarely  crystal,  usually  massive,  fibrous, 
lamellar. 


ROCK-FORMING   MINERALS.  3* 

H.  5.5  ;  Gr.  3.1-3.3.  Luster  on  cleavages  subpearly-vitre- 
ous  (metalloidal  in  bronzite).  Color  grayish,  yellowish,  or 
greenish  white,  olive-green,  brown ;  by  transmitted  light 
enstatite  is  grayish-yellowish  white,  and  bronzite  yellowish,, 
greenish.  Streak  uncolored-grayish.  Translucent-nearly 
opaque. 

Bp.  Fus.  6.     Chem.  Insoluble  in  HC1. 

(a)  Enstatite.     Comp.   MgSiO3 ;   color  white  with  shades 
of  yellow,  green,  and  gray.    Luster  vitreo-pearly.    Gr.  3.10- 

3-13- 

(b)  Bronzite.      (Magnesia  -  iron.       Enstatite).      Comp. 
(Mg,Fe)SiO3.     Color  grayish  or  olive-green,  brown.     Luster 
of  cleavages  adamantine-pearly  (the  stibmetallic  or  bronzy 
luster  that  gives  it  its  name  is  not  essential,  as  it  is  the  result 
of  alteration).     It   is   intermediate    between    enstatite   and 
hypersthene,  and  has  Gr.  up  to  3.3. 

The  enstatites  are  found  massive  in  gabbro,  norite,  granu- 
lar peridotites,  and  the  derived  serpentine.  Crystals  are 
rare  and  found  in  porphyritic  rocks  with  monoclinic  pyrox- 
ene ;  also  in  trachytes  and  andesites,  and  in  schists.  They 
alter  to  talc,  serpentine,  and, 

Bastite  (Schiller  Spar).  H.  3.5-4;  Gr.  2.5-2.7.  This 
comes  mostly  from  bronzite  and  shows  highly  its  peculiar 
luster  (schiller).  It  occurs  in  granular  eruptives  and  is  com- 
pletely decomposed  by  H2SO4 . 

26.  Hypersthene.  (Iron-magnesia  Enstatite.)  Some- 
times tabular,  usually  foliated,  massive,  crystals  rare,  some- 
times in  thin  prisms. 

H.  5-6;  Gr.  3.40-3.50.  Luster  subpearly  on  cleavages, 
frequently  metalloidal.  Color  darker  shades  of  the  enstatite 
colors,  brownish  green,  grayish  black,  greenish  black  ;  by 
transmitted  light,  light  red,  brown-red.  Translucent-nearly 
opaque  ;  streak  grayish,  brownish  gray.  Comp.  (Fe.Mg)SiO, 


32  MANUAL    OF  LITHOLOGY. 

and  sometimes  with  A12O3,  so  that  it  approximates  to 
the  aluminous  species  of  this  group. 

Bp.  Fuses  to  a  black  enamel,  and  gives  on  charcoal  a 
magnetic  mass.  Chem.  Partially  decomposed  by  HC1. 

Occurs  in  masses  in  gabbro,  norite ;  in  prisms  in  por- 
phyrites,  trachytes,  andesites,  and  lavas ;  not  found  in  true 
Archaean  rocks,  except  when  it  is  metachemized  ;  alters  to 
limonite,  hornblende,  actinolite,  bastite,  etc. 

Comparison  of  enstatite  (a),  bronzite  (£),  and  hypersthene 
(c) :  (a)  and  (b)  have  their  best  cleavage  parallel  to  the 
rhombic  prism  ;  have  generally  lighter  colors  and  lower 
specific  gravity  ;  are  almost  infusible  Bp.  and  untouched 
by  HC1.  (c)  has  the  best  cleavage  parallel  to  brachy- 
pinacoid ;  has  darker  colors  ;  is  fusible  and  partially  de- 
composed by  HC1.  (a)  and  (b)  are  often  fibrous,  (c)  not  so. 

'Monoclinic  Section. 

27.  Pyroxene.  Crystal,  lamellar,  granular,  rarely  fibrous 
or  columnar.  A  (m)  form  in  magmas  rich  in  alkalies  is  that 
of  an  hourglass. 

H.  5-6 ;  Gr.  3.2-3.6  (as  a  rock-former  never  less  than  3.3). 
Luster  vitreous-resinous,  sometimes  pearly.  Color  colorless 
through  greenish  or  yellowish  shades  to  brown  and  black. 
Streak  white-gray  or  grayish  green.  Transparent-opaque. 
Pyro-electric  ;  comp.  RSiO3,  R  being  commonly  protoxides 
of  Ca,  Mg,  and  Fe  ;  less  commonly  Mn  and  Zn ;  rarely  K 
and  Na,  and  in  small  per  cent ;  sometimes  also  sesquioxides 
of  Fe,  Mn,  and  Al.  Chem.  Generally  untouched  by  acids. 
The  varieties  are : 

NON-ALUMINOUS. 

(a)  Diopside  (Malacolite).  Slender  prismatic  crystals, 
columnar  masses.  Gr.  3.2-3.38.  Color  white  with  light 
shades  of  yellow,  gray,  and  green ;  also  dark  green  to  black 
(in  ferrous  varieties) ;  sometimes  transparent  and  colorless  ; 


ROCK-FORMING   MINERALS.  33 

by  transmitted  light  colorless  to  light  greenish  ;  sometimes 
brown.     Comp.  Ca,Mg(SiO6). 

Bp.  Fus.  3.75.  Occurs  sparingly  in  eruptives  (augite- 
granite,  diabase,  quartz-prophyry,  minette,  kersantite),  but 
widely  disseminated  in  Archaean  rocks  and  granular  lime- 
stones. 

(b)  Diallage.     Massive  lamellar,  thin   foliated,  generally 
not  crystal,  but  crystalline,  also  fibrous,  and  interlaminated 
with  an  orthorhombic  pyroxene. 

H.  4  ;  Gr.  3.2-3.35.  Luster  pearly,  sometimes  metalloidal. 
Color  greenish  shades  and  brown ;  like  diopside  by  trans- 
mitted light.  Comp.  also  like  it,  but  with  A12O3,  which 
makes  it  approach  augite.  Bp.  and  chem.  like  diopside. 

Necessary  in  gabbro  and  derivatives ;  essential  in  some 
peridotites  and  serpentines ;  sparingly  in  basaltic  and  ande- 
sitic  extrusions  in  prisms  ;  infrequent  in  Archasan  rocks,  and 
confined  to  olivine-bearing  massives  and  schists  and  their 
derivatives ;  metachemized  to  serpentine  and  chlorite ; 
metamorphosed  to  amphibole  on  gabbro-phyllite  contacts. 

ALUMINOUS. 

(c)  Augite.      (CaMgSiaOe)     with     (Mg,Fe)(Al,Fe)sSiO.. 
Usually  short  prismatic  crystals;  also  in  irregular  columns 
and  grains. 

H.  and  Gr.  as  first  given.  Color  greenish  or  brownish 
black  to  black;  by  transmitted  light  green,  brown,  rarely 
yellow,  red,  or  violet. 

Bp.  Fus.  3 ;  in  general  the  ferruginous  varieties  of  py- 
roxene give  a  magnetic  globule  on  charcoal,  and  the 
greenish  and  yellowish  kinds  become  reddish  brown  by 
heating  on  platinum  foil  from  the  formation  of  ferric  oxide. 

This  is  one  of  the  commonest  components  of  crystalline 
rocks.  In  the  extrusives  it  is  more  commonly  crystal;  in 
the  granitoid  massives  it  occurs  in  irregular  columns ;  not 


34  MANUAL   OF  LITHOLOGY. 

found  in  the  crystalline  schists  unless  the  greenish  mono- 
clinic  pyroxenes  in  them  are  augite  instead  of  a  dark  diop- 
side.  The  light  green  variety,  omphacite,  is  found  in  ec- 
logites  in  rounded  grains  or  short  columnar  aggregates. 

Pyroxene  is  necessary  in  the  basalt-gabbro  series,  and 
essential  in  many  rocks.  Diallage  is  necessary  in  gabbro. 
Pyroxene  alters  to  chlorite  and  thence  to  carbonates, 
limonite,  clay,  and  quartz ;  by  uralitization  to  hornblende,, 
to  talc,  serpentine,  epidote,  glauconite,  mica.  According 
to  Rosenbusch,  the  pyroxenes  in  acid  and  alkaline  rocks 
are  green,  in  basic  extrusives  brown,  in  crystalline  schists 
colorless  to  greenish. 

28.  Acmite.     (^Egerite.)     (Lime-soda  Pyroxene.)     Long 
prisms. 

H.  6-6.5  ;  Gr.  3.50-3.55.  Luster  vitreous-resinous.  Streak 
pale  yellowish  gray.  Color  brownish  or  reddish  brown, 
green ;  by  transmitted  light  green,  brown  to  violet.  Sub- 
transparent-opaque.  Comp.  Naa(Fe2)Si4O12. 

Bp.  Fus.  2  to  lustrous  black  magnetic  globule,  coloring 
the  flame  deeply  yellow ;  with  fluxes  reacts  for  Fe  and  Mn. 
Chem.  Slightly  acted  on  by  acids. 

Occurs  in  elseolite-syenite  and  augite-syenite  of  Canada, 
New  Jersey,  and  Norway  ;  in  sodalite-granite  of  Greenland, 
at  Ditro ;  in  acid  lavas  of  San  Miguel,  Azores  ;  in  alkaline 
granites  rich  in  soda,  acmite- trachyte,  etc. 

Triclinic  Section. 

29.  Hiortdahlite.     Crystals  tabular  and  vertically  elon- 
gated. 

H.  5-5.6;  Gr.  3.267.  Luster  vitreous  on  crystal  faces, 
greasy  on  fractures.  Color  light  shades  of  straw-,  sulphur-, 
to  honey-yellow  ;  less  often  yellowish  brown.  Comp.  nearly 
4Ca(Si,Zr)O3.Na2ZrO,F2.  Bp.  Fus.  easily  to  yellowish  white 
enamel.  Chem.  Gelat.  with  acids.  The  crystals  are  5-10  mm. 


ROCK-FORMING   MINERALS.  35 

iong  and  2-3  mm.  broad,  and  resemble  wohlerite ;  but  gr.  is 
lower,  bp.  fuses  more  easily.  Occurs  in  elaeolite-syenite  in 
Norway. 

THE  AMPHIBOLES. 

These  dark-colored  bisilicates  rank  next  to  the  pyroxenes 
in  wideness  of  diffusion,  and  like  them  are  grouped  in  the 
same  crystallographic  systems.  There  are  fewer  species 
than  in  the  former  group ;  but  these  show  close  parallels 
with  similar  pyroxenes.  The  prismatic  angles  are  56°  and 
124° ;  the  other  differences  will  be  discussed  later. 

Orthorhombic  Section. 

30.  Anthophyllite.  Crystals  rare,  unterminated  prisms, 
commonly  lamellar  and  without  definite  boundaries,  fibrous 
massive,  with  slender  fibers^  in  prismatic  aggregates  like 
actinolite. 

H.  5.5-6;  Gr.  3.15-3.24.  Luster  vitreo-pearly  on  cleav- 
ages. Color  grayish,  yellowish,  and  greenish  brown, 
emerald-green,  sometimes  metalloidal.  Streak  uncolored  or 
grayish.  Transparent-translucent.  Comp.  (Mg,Fe)SiO8,  or 
like  the  enstatite-hypersthenes. 

Bp.  Fusible  with  difficulty  to  a  black  magnetic  enamel ; 
reacts  for  Fe  with  fluxes.  Chem.  Untouched  by  acids. 
Varieties : 

(a)  Anthophyllite  (Mg-Fe- Anthophyllite).     Prismatic  angle 
54°  23' ;  corresponds  to  enstatite. 

(&)  Gedrite  (Al-Fe-Mg-Anthophyllite).  Prismatic  angle 
54°  40' ;  corresponds  to  hypersthene. 

These  are  generally  restricted  to  the  hornblende  gneisses 
and  schists  among  unaltered  rocks ;  occurs  abundantly  in 
olivine  serpentines.  Alteration  products  unknown. 


3  MANUAL   OF  LITHOLOGY. 

Monoclinic  Section. 

31.  Amphibole.  Prismatic,  columnar,  fibrous,  rarely  la- 
mellar, granular-massive. 

H.  5-6;  Gr.  2.9-3.4.  Fracture  subconchoidal,  uneven. 
Brittle.  Luster  vitreous.  Color  from  black  to  white 
through  shades  of  green  and  brown,  rarely  reddish, 
yellowish.  Sometimes  transparent,  usually  translucent. 
Varieties : 

SLIGHTLY  OR  NON-ALUMINOUS. 

(a)  Tremolite  (Ca-Mg-Amphibole).     Crystals  long-bladed 
and  short  and  stout,  thin  columnar,  fibrous,  compact  granu- 
lar massive. 

H.  5-6;  Gr.  2.9-3.16.  Color  white  to  dark  gray;  color- 
less by  transmitted  light.  Occurs  in  Archaean  granular  lime- 
stone, in  altered  olivine  rocks  and  serpentines.  Alters  to 
talc. 

(b)  Actinolite  (Ca-Mg-Fe-Amphibole).   Prismatic  individu- 
als, columnar  and  fibrous  aggregates,  granular-massive. 

Gr.  3-3.2.  Sometimes  transparent.  According  to  thick- 
ness and  arrangement  of  fibers  it  is  glassy,  asbestiform,  and 
•radiated ;  color  green  from  ferrous  iron,  and  same  by  trans- 
mitted light.  Occurs  principally  in  Archasan  basic  schists ; 
necessary  in  actinolite-schist ;  also  in  metachemized  diabase 
and  gabbro.  The  Smaragdite  in  saussurite-gabbro  is  a 
slightly  aluminous  actinolite. 

{c)  Asbestus  is  a  finely  fibrous  tremolite,  actinolite,  or 
other  slightly  or  non-aluminous  amphibole. 

(d)  Uralite  is  a  paramorph  of  hornblende  after  pyroxene, 
in  which  the  crystals  have  the  habit  of  the  latter  and  the 
cleavage,  gr.,  and  optical  characteristics  of  the  former.  Oc- 
curs in  diabase,  diabase-porphy  rites  interbedded  with 
schists,  augite-diorite,  augite-syenite,  etc. 


ROCK-FORMING   MINERALS.  37 

(e)  Nephrite  (Jade)  is  a  compact  and  fine-grained  tremo- 
lite  or  actinolite.  H.  6-6.5  5  Gr.  2.96-3.1.  Fracture  splin- 
tery. Luster  glistening.  Occurs  in  eastern  Siberia  and 
New  Zealand. 

ALUMINOUS. 

32.  Hornblende  (Pargasite)  (Al-Fe-Mg-Ca-Amphibole). 
Crystals,  prismatic  individuals.  The  lighter  green  kinds  are 
sometimes  called  pargasite  and  the  darker  ones  hornblende  ; 
but  E.  S.  Dana  says  that  no  line  can  be  drawn  between  them 
from  this  or  any  other  characteristic.  Gr.  3.05-3.47.  Color 
green,  bluish  green,  greenish  black,  black.  Varieties  : 

(a)  Ordinary   hornblende    with    color   generally    green, 
sometimes  deep  brown  and  brownish  red.     Occurs  in  por- 
phyritic  states   of   granite,  syenite,  and  diorite ;    granular 
massives   of   the  Archaean.     Alters   to  chlorite,  thence   to 
clay,  carbonates,  limonite,  and  quartz. 

(b)  Basaltic    hornblende    with    color   black ;    by    trans- 
mitted light   brown  in  all  directions.     Always   in  crystals. 
Becomes  greenish  on  altering.    Occurs  only  in  porphyritic 
extrusives.    The  bp.  and  chem.  tests  are  as  in  pyroxene. 

33.  Arfvedsonite    (Al-Na-Amphibole).     Imperfect  crys- 
tals and  massive. 

H.  5.5-6  ;  Gr.  3.44.  Luster  vitreous.  Color  pure  black, 
in  thin  scales  deep  green  or  brown.  Streak  grayish  green. 
Opaque,  except  in  thin  splinters.  Fracture  subconchoidal. 

Bp.  Fuses  at  2  with  intumescence  to  a  black  magnetic 
globule  ;  colors  the  flame  yellow  (soda),  and  reacts  with 
fluxes  for  Fe  and  Mn.  Chem.  Not  touched  by  acids. 
Comp.  about  4Na2O,3CaO,i42FeO,(Al,Fe)3O3,2iSiO2.  Oc- 
curs in  elseolite-syenites  and  other  rocks  poor  in  silica  and 
rich  in  soda. 

34.  Glaucophane  (Al-Na-Amphibole).    Commonly  mass- 
ive fibrous,  or  columnar  to  granular. 


38  MANUAL    OF  LITHOLOGY. 

H.  6-6.5;  Gr-  3.103-3.044.  Luster  vitreous  to  pearly. 
Color  azure-blue,  lavender-blue,  bluish  black,  grayish. 
Streak  grayish  blue.  Translucent.  Fracture  conchoidal 
to  uneven.  Brittle.  Comp.  NaAl(SiO3)2(Fe,Mg)SiO3.  Pris- 
matic cleavage  angle  58°  16'.  Recognized  by  its  blue  color. 
Occurs  in  glaucophane-schist ;  less  frequently  in  mica- 
schist,  gneiss,  eclogite  ;  altered  from  diallage. 

35.  Riebeckite  (Fe-Na-Amphibole).     Unterminated  pris- 
matic crystalloids. 

H.  5-6;  Gr.  3.3.  Luster  vitreous.  Color  black.  Comp. 
2Na2Fe(SiO3)2.FeSiO3,  corresponding  closely  to  acmite  (28). 
Prismatic  cleavage  56°  perfect.  Occurs  in  keratophyre, 
quartz-keratophyre,  and  minette,  gneiss,  soda  granite. 

36.  iEnigmatite  (Cossyrite).      Prismatic  crystals  ;   angle 
66°. 

H.  5-6 ;  Gr.  3.80  (^Enig.),  3.74  (Coss.).  Luster  vitreous. 
Color  black  ;  brownish  black  by  transmitted  light.  Streak 
reddish  brown.  Translucent  to  opaque.  Comp.  titano-sili- 
cate  of  ferrous  iron  and  sodium,  with  sesquioxides  of  iron 
and  alumina. 

Bp.  Fusible  easily  to  brownish-black  glass.  Chem. 
Partly  decomposed  by  acids.  ^Enigmatite  occurs  in  large 
crystals  in  the  elseolite-syenite  of  Norway  ;  cossyrite  in 
small  crystals  in  the  rhyolite  lavas  of  the  island  of  Pantel- 
leria. 

COMPARISON   OF  THE   PYROXENE   AND  AMPHIBOLE   GROUPS. 

Prismatic  angle  with  pyroxene  87°  and  93°  ;  with  amphi- 
bole  56°  and  124°.  Prismatic  cleavage  more  distinct  in  am- 
phibole.  Crystals  in  pyroxene  stouter,  and  the  massive  kinds 
lamellar  and  granular;  in  amphibole  they  are  long,  pris- 
matic, and  fibrous.  In  corresponding  kinds  the  gr.  is  one 
tenth  higher  in  pyroxene.  Pyroxene  has  more  lime  ;  amphi- 
bole more  magnesia  and  alkalies.  Of  the  rock-makers  the  gr. 


ROCK-FORMING   MINERALS.  39 

of  pyroxene  is  never  less  than  3.3  ;  that  of  amphibole  al- 
ways so.  Amphibole  is  associated  with  the  more  acid  rocks, 
soda  and  potash  feldspars,  potash  mica,  and  pyrite  ;  pyr- 
oxene with  basic  rocks,  leucite,  olivine,  and  labradorite. 
That  they  are  closely  isomorphous  is  shown  by  the  fact  that 
of  twinned  forms  one  is  frequently  pyroxene  and  the  other 
amphibole. 

THE   EPIDOTES. 

37.  Zoisite  (Ca  Al-Epidote).  Orthorhombic,  crystal, 
prismatic  aggregates,  massive,  compact. 

H.  6-6.5  ;Gr.  3-25-3-37-  Luster  vitreous  and  pearly  on 
most  perfect  cleavage.  Color  grayish  white,  gray,  yellowish 
brown,  greenish  gray,  apple-green ;  also  shades  of  light 
red ;  by  transmitted  light  colorless,  gray,  greenish  gray. 
Comp.  HCa2Al3Si3O13.  It  graduates  into  epidote  by  the 
addition  of  iron. 

Bp.  Fusible  at  3.5  with  intumescence  to  a  white  blebby 
mass  and  gives  much  water.  Chem.  Undecomposed  by  acids 
unless  previously  heated  to  redness,  and  then  gelatinizes 
with  HC1.  Occurs  in  the  crystalline  hornblende-schists. 
The  variety 

(a)  Saussurite  is  compact  and  tough  with  splintery 
fracture.  H.  6.5-7;  Gr.  3-3.4.  Color  white  to  gray  with 
greenish  shades.  Translucent  to  opaque.  Not  homoge- 
neous, but  the  result  of  dynamo-metamorphism  of  a  plagio- 
clase.  With  smaragdite  forms  euphotide ;  also  present  in 
saussurite-gabbro. 

This  name  has  also  been  applied  to  forms  of  garnet, 
meionite,  labradorite.  Many  European  authorities  place  it 
under  labradorite ;  J.  D.  Dana,  from  its  high  gr.,  and  Sterry 
Hunt,  from  its  chem.  comp.,  put  it  as  above.  They  are  fol- 
lowed by  Zirkel,  who  names  authorities  of  the  same  opinion  ; 
Rosenbusch  puts  it  under  epidote. 


4O  MANUAL    OF  LITHOLOGY. 

38.  Epidote     (Ca-Al-Fe-Epidote).       Monoclinic,   seldom 
sharply  defined  crystals,  usually  fibrous-granular-massive. 

H.  6-7;  Gr.  3.25-3.5.  Luster  vitreous,  but  pearly  to  resin- 
ous on  the  orthopinacoid.  Color  shades  of  green  to  black  ; 
also  red,  yellowish,  gray ;  by  transmitted  light  colorless, 
pale  yellow,  rarely  yellowish  brown,  pale  green,  seldom 
red.  Comp.  HCaa(Al,Fe3)Si3O13.  The  greater  density  over 
zoisite  is  due  to  iron. 

Bp.  Water  in  closed  tube  on  strong  heating ;  fusible  at 
3-3.5  with  intumescence  to  dark  brown  or  black  mass  ;  mag- 
netic in  the  darker  shades ;  gives  iron  with  the  fluxes. 
Chem.  Decomp.  by  fus.  with  alkaline  carbonates,  and  by  HC1 
with  gelatinization  after  heating  to  redness ;  otherwise  un- 
touched by  acids. 

The  commonest  of  metachemic  minerals,  and  seldom,  if 
ever,  occurs  as  an  original  component  in  rocks.  (Keyes 
thinks  that  the  occurrence  of  epidote  with  allanite  in  the 
Maryland  granite  shows  it  to  be  a  primary  mineral.) 
Occurs  in  crystalline  massives  and  schists  as  an  alteration  of 
the  iron-amphiboles,  as  granite,  syenite,  mica-  and  horn- 
blende-schists, serpentine,  etc.  Alters  with  difficulty,  as  all 
the  elements  have  peroxidized.  Variety  : 

(a)  Piedmontite  (Mn-Epidote).  Gr.  3.404.  Bp.  Fusible 
at  3.5  to  a  lustrous  glass  ;  otherwise  like  epidote.  Common 
in  the  crystalline  schists  of  Japan  and  altered  pre-Cambrian 
rhyolites  of  Pennsylvania  and  Maryland. 

39.  Allanite    (Cerium,  etc.,  Epidote).     Tabular  crystals, 
massive,  granular. 

H.  5.5-6;  Gr.  3.5-4.2.  Brittle.  Fracture  uneven.  Luster 
submetallic,  pitchy,  resinous.  Color  dark  brown  to  black 
with  shades  of  green  and  yellow ;  by  transmitted  light 
reddish  brown,  greenish  brown.  Subtranslucent  to  opaque. 
Comp.  like  epidote,  but  with  partial  substitution  of  Fe  for 
Ca,  and  Ce,  La,  Di,  Y,  and  Er  for  AL 


ROCK-FORMING   MINERALS.  41 

Bp.  More  or  less  water  on  strong  heating  in  closed  tube; 
fus.  2.5  with  results  like  epidote  ;  reacts  for  Fe  with  fluxes. 
Chem.  Unlike  epidote  and  zoisite,as  it  gelatinizes  with  HC1 
only  before  ignition ;  untouched  after.  Occurs  in  gneiss, 
granite,  granite-porphyry,  quartz-porphyry,  diorite-porphy- 
rite,  andesite,  rhyolite,  dacite.  Alters  with  yellow  crust, 
but  generally  fresh  in  rocks. 

LEUCITE-NEPHELINE-SODALITE    GRO UP. 

These  are  silicates  more  or  less  common  to  eruptives. 
containing  the  black  bisilicates.  They  are  found  with,  and 
more  or  less  replace,  the  plagioclases  in  them.  All  have 
H.  5-6  ;  Gr.  2.14-2.6. 

40.  Leucite.     Tetragonal  at  ordinary  temperatures,  but 
isometric   at    500°    C.    commonly   crystal,  in  disseminated 
grains,  rarely  massive. 

H.  5.5-6;  Gr.  2.45-2.50.  Luster  vitreous.  Color  white, 
grayish.  Translucent  to  opaque.  Comp.  KAl(SiaO6). 

Bp.  Infusible ;  gives  blue  of  Al  with  cobalt  solution. 
Chem.  Slightly  attacked  by  HC1  in  the  solid,  but  decomp. 
without  gelat.  when  powdered.  Occurs  in  Tertiary  and 
post-Tertiary  extrusives ;  in  older  rocks  metachemized  to 
allied  forms;  found  in  leucite-basalts,  leucite  rock, phonolite,. 
etc.;  is  not  found  with  free  quartz.  Alters  to  feldspar, 
nepheline,  and  kaolin. 

41.  Nepheline  (Elseolite).     Hexagonal,  stout,  prismatic, 
thin-columnar,  granular-massive,  compact. 

H.  5.5-6;  Gr.  2.55-2.65.  Fracture  subconchoidal.  Brit- 
tle. Luster  vitreous  to  greasy.  Color  colorless,  yellowish 
(nepheline),  and  when  massive  greenish  and  reddish  shades 
(elaeolite).  Comp.  K2Na2AlaSi2O8. 

Bp.  Fus.  3.5  quietly  to  a  clear  glass.  Chem.  Gelatinizes 
with  acids. 

Nepheline  bears  the  same  relation  to  elseolite  that  sani- 


42  MANUAL    OF  LITHOLOGY. 

dine  does  to  orthoclase,  and  both  are  found  under  similar 
conditions. 

(a)  Nepheline  is  the  glassy  crystalline  form  found  in  the 
younger  effusives,  and  with  Gr.  2.56.    Occurs  in  phonolites, 
nepheline-basalts,  and  with  sanidine. 

(b)  Elceolite  is  the  coarser  crystalline  and  generally  mas- 
sive form,  variously  colored,  that  occurs  in  older  intrusive 
rocks,  and  frequently  associated  with  orthoclase.     Gr.  2.59- 
2.65.    Occurs   in  elaeolite-syenite,  miascite,   ditroite,  augite 
syenite. 

Both  alter  to  thomsonite,  analcite,  sodalite,  natrolite, 
pinite,  and  kaolin. 

42.  Cancrinite.     Hexagonal,  usually  massive. 

H.  5-6 ;  Gr.  2.42-2.5.  Color  white  to  gray,  yellow,  green, 
blue,  reddish ;  by  transmitted  light  colorless.  Luster  sub- 
vitreous  with  pearly  or  greasy  film.  Transparent  to  trans- 
lucent. Comp.  4NaaO,4Al2O3,9SiO2  +  2CaO,CO2  +  sHaO. 

Bp.  Water  in  closed  tube  ;  fuses  at  2  with  intumescence 
and  loss  of  color  to  a  white  blebby  glass  (being  thus  distin- 
guished from  nepheline).  Chem.  Effervesces  with  HC1,  and 
after  heating  forms  a  jelly.  Occurs  in  elseolite-syenite. 
Alters  to  natrolite. 

43.  Sodalite.     Isometric,  prisms,  grains,  massive. 

H.  5.5-6;  Gr.  2.14-2.30.  Luster  vitreous-greasy.  Color 
white  and  light  shades  of  green,  blue,  yellow,  and  red  ;  shows 
the  same  by  transmitted  light  and  colorless.  Comp. 
Na4(AlCl)Al,Si3Oia. 

Bp.  In  closed  tube  the  blue  kinds  become  white  and 
opaque  ;  fuses  at  3.5-4  with  intumescence  to  a  colorless  glass, 
and  with  microcosmic  salt  and  oxide  of  copper  gives  bluish 
flame-coloration  due  to  chlorine.  Chem.  Decomp.  by 
HC1  with  separation  of  gelatinous  silica.  Occurs  as  es- 
sential in  elaeolite-syenite  ;  crystallizes  in  rocks  after  augite 


ROCK-FORMING   MINERALS.  43 

and  before  nepheline  and  the  feldspars ;  alters  to  thomsonite, 
muscovite,  natrolite,  and  kaolin. 

44.  Haiiyne.     Isometric,  rounded  grains. 

H.  5.5-6;  Gr.  2.4-2.5.  Fracture  flat-conchoidal.  Brittle. 
Luster  vitreous-greasy  (like  sodalite  and  nepheline).  Color 
bright  shades  of  blue  and  green,  red,  yellow ;  by  trans- 
mitted light  the  same  and  colorless.  Subtransparent-trans- 
lucent.  Comp.  2(Na3O,Al9O2,2SiO2)  +  Na2O,SO3,  with  Na 
partly  replaced  with  Ca.  There  are  two  varieties  : 

(a)  Haiiyne  with  considerable  Ca.     Bp.  Retains  its  color 
in  closed  tube,   and   is   thus   distinguished    from   sodalite ; 
fuses  at  4.5  to  white  glass  ;  gives  sulphur  reaction  with  soda 
on  charcoal.     Chem.    Decomposed  by  HC1  with  separation 
•of  gelatinous  silica. 

(b)  Nosean  (Soda  Haiiyne). 

H.  5.5  ;  Gr.  2.25-2.4.  Color  grayish,  bluish,  brownish, 
black.  Translucent-opaque.  Otherwise  like  haiiyne,  except 
that  hauyne  gives  H3S  on  heating  with  HaSO4,  and  has  the 
stronger  blue  color;  but  nosean  takes  a  bright  blue  on  heat- 
ing, owing  to  a  change  in  the  sodium  sulphide.  The  red 
•color  of  hauyne  is  due  to  ferric  scales.  Occurs  in  basalt, 
phonolite,  and  extrusives  poor  in  quartz  and  alkali. 

45.  Melilite.     Tetragonal,  usually  in  short  square  prisms, 
also  in  irregular  grains. 

H.  5  ;  Gr.  2-3.10.  Luster  vitreous.  Color  white,  shades 
of  yellow  and  brown.  Translucent  to  opaque.  Comp. 
(Ca,Mg)s(Al,Fe)aSi.019. 

Bp.  Fuses  at  3  to  a  yellowish  greenish  glass ;  gives  Fe 
with  fluxes.  Chem.  Gelatinizes  with  HC1.  Occurs  in  the 
extrusives  and  abundant  in  leucite  and  nepheline  rocks,  and 
often  replaces  the  feldspars  so  as  to  be  necessary  to  the 
species. 

46.  Olivine    (Chrysolite,  Peridot).     Orthorhombic,  usu- 


44  MANUAL    OF  LITHOLOGY. 

ally  in  imbedded  grains,  massive  and  compact  or  granular;. 
The  precious  form  (chrysolite)  is  not  a  rock-former 

H.  6.5-7;  Gr.  3.3-3.45.  Luster  vitreous.  Color  commonly 
olive-green  and  changing  to  yellowish  brown  or  red  on 
oxidation  of  the  iron  ingredients ;  by  transmitted  light 
colorless  to  greenish  white.  Comp.  (Mg,Fe)2SiO4. 

Bp.  Whitens,  but  is  infusible  ;  reacts  for  iron  with  fluxes. 
Chem.  Decomposed  by  HC1  and  H,SO4  with  separation  of 
gelatinous  silica.  Alters  to  carbonates,  silicates,  serpentine, 
limonite,  and  in  Archaean  rocks  to  amphiboles.  Occurs  in 
basic  granular  eruptives  and  basic  crystalline  schists  ;  some- 
times accessory  and  sometimes  essential  and  necessary. 
Varieties : 

(a)  Hyalosiderite    (Ferruginous   Olivine).     Gr.  3.57.    Bp. 
Fuses  to  a  black  magnetic  globule ;  otherwise  like  olivine. 

(b)  Fayalite  (I ro n-oli v i ne).  Gr.  4-4.14.    Luster  metalloidal. 
Color  light  yellow  to  black  through  shades  of  brown  due  to- 
oxidation.    Comp.  Fe2SiO4.    Bp.  Fuses  easily  to  a  magnetic 
globule ;    otherwise    like    olivine.      Occurs    in    extrusives, 
among  them  rhyolite  from  Yellowstone  Park. 

Olivine  is  distinguished  from  quartz  by  its  yielding  to- 
acids,  fusibility,  and  Fe  reaction  with  borax. 

SERPENTINE-TALC   GROUP. 

47.  Serpentine.  Monoclinic,  in  pseudomorphs,  some- 
times foliated  and  fibrous,  usually  amorphous. 

H.  2.5-4 (rarely  5.5);  Gr.  2.50-2.65.  Luster  feebly  greasy, 
waxy.  Color  shades  of  green  and  brownish  yellow,  some- 
times nearly  white  ;  by  transmitted  light  transparent  with 
shades  of  green  and  yellow.  Translucent-opaque.  Comp, 

H(MgsSi,0.. 

Bp.  gives  water ;  fus.  6  on  edges  ;  reacts  for  Fe.  Chem. 
Decomposed  by  HC1  and  H3SO4,  and  more  vigorously  in 
proportion  to  the  heat  of  the  acids.  Widely  distributed 


ROCK-FORMING   MINERALS.  45 

.and  frequently  in  large  masses,  and  results  from  the  altera- 
tion of  peridotite  and  other  rocks. 

Serpentine  is  distinguished  from  pyrophyllite  and  talc 
by  its  complete  decomp.  by  HaSO4,  pyrophyllite  being  only 
partially  decomp.,  talc  not  at  all.  Talc  gives  a  red  color 
(Mg)  with  cobalt  solution  on  heating,  while  pyrophyllite 
gives  blue  (Al). 

48.  Talc.     Orthorhombic  or  monoclinic,  usually  foliated, 
massive,  also  granular-massive. 

H.  1-1.5;  Gr.  2.7-2.8.  Sectile.  Thin  laminae,  not  elastic. 
Luster  pearly.  Color  shades  of  green  from  white  to  blackish. 
Comp.  H,Mg3Si4012. 

Bp.  gives  water  generally  after  hard  heating ;  whitens, 
exfoliates;  fuses  at  5.5  on  thin  edges  to  a  white  enamel;  red 
color  (Mg)  on  heating  with  cobalt  solution,  and  is  thus  dis- 
tinguished from  muscovite.  Chem.  Not  decomposed  by 
acids  ;  important  in  crystalline  and  metamorphic  schists. 

49.  Pyrophyllite.      Monoclinic,    foliated,    granular-com- 
pact or  cryptocrystalline. 

H.  1-2  ;  Gr.  2.28-2.9.  Color  rather  more  yellowish  than 
talc.  Comp.  H2AlaSi4O12  (an  aluminous  talc). 

Bp.  Water  at  high  temperature;  whitens  and  fuses  at  6 
on  thin  edges  ;  radiated  variety  exfoliates ;  gives  blue  color 
(Al)  with  cobalt  solution.  Chem.  Partly  decomposed  by 
H2SO4  and  completely  by  fusion  with  alkaline  carbonates. 
Occurs  in  crystalline  schists. 

The  two  following  minerals  are  found  generally  in  erup- 
tives  in  microscopic  proportions,  and  are  among  the  first  to 
crystallize.  Their  crystals  are  therefore  included  in  those 
formed  later.  They  also  occur  of  macroscopic  proportions. 

50.  Zircon.     Tetragonal,  crystal,  never  massive. 

H.  7.5;  Gr.  4.68-4.70.  Luster  adamantine.  Color  color- 
less to  brownish  shades  of  yellow;  by  transmitted  light, 


46  MANUAL    OF  LITHOLOG  Y. 

light  yellow,  pink,  and  violet.  Transparent-opaque.  Comp. 
ZrSiO4. 

Bp.  Infusible;  not  acted  on  by  microcosmic  salt;  de- 
composed when  powdered  and  fused  with  soda  on  a  plat- 
inum wire,  and  gives  with  turmeric  paper  the  orange  color 
for  Zr  when  treated  with  HC1.  Chem.  When  powdered  is 
decomposed  by  hot  H3SO4 ;  otherwise  not  attacked ;  de- 
comp.  by  fusion  with  alkaline  carbonates  and  bisulphates. 
Occurs  in  almost  all  eruptives  and  Archaean  rocks — in  the 
former  it  is  one  of  the  first  intratelluric  crystals  ;  abundant 
in  granite,  syenite,  and  gabbro  ;  necessary  in  zircon-syenite. 

51.  Apatite.  Hexagonal,  columnar  in  eruptives,  usually 
slender,  but  infrequently  short  and  stout,  granular,  in  crys- 
talline schists  massive. 

H.  4.5  (massive),  otherwise  5  ;  Gr.  3.17-3.23.  Luster 
vitreous-subvitreous.  Color  usually  shades  of  green,  some- 
times variously  colored ;  usually  colorless  by  transmitted 
light.  Transparent-opaque.  Comp.  3Ca3P2O8  +  Ca(F,Cl)a. 
Rosenbusch  says  that  all  rocks  contain  apatite  ;  more  abun- 
dant in  the  granular  eruptives  and  feldspathic  crystalline 
schists  of  acid  types. 

THE   ZEOLITES. 

These  form  amygdaloids  in  the  vesicular  cavities  of 
effusives,  and  replace  other  minerals  in  compact  states  by 
metachemism.  They  are,  therefore,  all  secondary  minerals 
and  of  little  importance  as  rock-formers.  Analcime  is  the 
only  one  that  gives  its  name  to  a  rock.  In  some  cases  they 
furnish  by  their  composition  an  idea  of  the  components 
(chemical)  of  a  compact  rock.  They  are  all  hydrous  silicates 
of  alumina  with  alkalies  and  alkaline  earths,  and  can  be 
divided  into : 

(a)  Lime  zeolites :  Heulandite,  epistilbite,  laumontite 
(all  monoclinic). 


ROCK-FORMING   MINERALS.  47 

(&)  Lime-soda  zeolites  :  Stilbite  (monoclinic)  and  chaba- 
zite  (rhombohedral). 

(V)  Lime-potash  zeolite :  Phillipsite  (monoclinic). 

(d)  Barium-potash  zeolite :  Harmotome  (monoclinic). 

(e)  Soda    zeolites :    Analcite    (isometric)    and    natrolite 
(orthorhombic). 

Analcite  generally  shows  the  presence  of  nepheline  or 
leucite,  as  it  is  altered  from  them. 

The  following  species  are  found  mostly  in  metamorphic 
rocks  and  crystalline  schists.  Some  are  found  sparingly  in 
eruptives ;  others  never  occur  there.  They  are  grouped 
according  to  their  chemical  composition. 

SILICATES. 

52.  Scapolite  (Wernerite).   Irregular  grains,  fibrous,  lath- 
shaped  aggregates. 

H.  5.5  ;  Gr.  2.569-2.735.  Luster  vitreous-pearly  to  res- 
inous. Color  white  gray  bluish,  greenish,  reddish,  all  in 
light  shades,  but  colorless  and  transparent  when  fresh. 
Fracture  subconchoidal.  Brittle. 

Bp.  Fus.  easily  with  intumescence  to  a  white  blebby 
glass.  Chem.  Imperfectly  decomposed  by  HC1.  Occurs 
in  metamorphic,  but  not  primary,  rocks. 

53.  lolite  (Cordierite).     Orthorhombic,  crystal,  irregular 
grains. 

H-  7-7.5  ;  Gr.  2.60-2.66.  Luster  vitreous.  Color  shades 
of  blue ;  colorless  by  transmitted  light,  rarely  yellowish, 
blue,  violet.  Transparent-translucent.  Comp.  H2(Mg,Fe)4- 
Al8SiIOO,,. 

Bp.  Loses  transparency  and  fusible  5-5.5.  Chem.  Par- 
tially decomposed  by  acids ;  decomposed  by  fusion  with  al- 
kaline carbonates.  Occurs  most  commonly  in  gneiss  and 
the  crystalline  schists  ;  less  commonly  in  granite,  quartz- 
porphyry,  andesites. 


4  MANUAL    OF  LITHOLOGY. 

54.  Garnet     Isometric,  crystal,  granular-massive. 

H,  6.9-7.5;  Gr.  3.15-4.3.  Luster  vitreous  to  resinous. 
Color  white  to  black  through  red,  brown,  yellow,  green. 
Transparent  to  subtranslucent.  Comp.  an  orthosilicate 
with  interchangeable  bivalent  (Ca,Mg,Fe,Mn)  and  trivalent 
(Al,Fe,Cr,Ti)  elements,  as  follows : 

(a)  Grossularite  (Ca-Al-Garnet)  (Cinnamon  Stone). 

Gr.  3.55-3.66.  White,  yellow,  brown,  red,  green  ;  color- 
less by  transmitted  light.  Occurs  in  Archaean  granular  lime- 
stone and  lime-silicate-hornstones. 

(b}  Pyrope  (Mg-Al-Garnet)  (Bohemiam  Garnet). 

Gr.  3.70-3.75.  Red  to  nearly  black ;  blood-red  by  trans- 
mitted light.  Transparent  and  a  gem.  Occurs  in  peridotites 
and  their  derivatives. 

(c)  Almandite  (Fe-Al-Garnet)  (Oriental  Garnet). 

Gr.  3.9-4.2.  Color  red  in  precious  garnet,  black  in  the 
common  variety;  red  by  transmitted  light.  Occurs  in  granite 
rocks,  andesites  ;  most  abundant  in  gneiss  and  Archaean  rocks 
without  feldspar. 

(d)  Spessartite  (Mn-Al-Garnet). 

Gr.  4-4.3.  Color  dark  red,  brownish  red  ;  by  transmitted 
light  blood-red,  yellowish  red,  and  colorless,.  Occurs  in 
rhyolite. 

(e)  Andradite  (Ca-Fe-Garnet)   (Common    Garnet,    Black 
Garnet). 

Gr.  3.8-3.9.  Variously  colored,  but  not  white  ;  brown  by 
transmitted  light.  Occurs  generally  in  metamorphic  schists. 

(/)  Uvarovite  (Ca-Cr-Garnet). 

H.  7.5  ;  Gr.  3.41-3.52.  Color  emerald-green.  From  the 
Ural  Mountains,  etc. 

Bp.  Fusible  generally  to  a  light-brown  to  black  glass  at 
3  in  (a),  (c),  (d),  3.5  in  (b),  and  6  in  (/) ;  most  kinds  react  for 
Fe.  Chem.  All  partially  decomposed  by  acids ;  all,  except 
(/),  decomp.  by  HC1  after  ignition,  and  generally  with  sep- 


ROCK-FORMING   MINERALS.  49 

aration  of  gelatinous  silica  ;  decomposed  by  fusion  with 
alkaline  carbonates.  Plentiful  in  eruptives,  but  most  com- 
mon in  metamorphic  schists  of  all  kinds,  in  serpentine, 
granular  and  crystalline  limestones. 

55.  Vesuvianite.     Tetragonal,  in    irregular   shapes    and 
prismatic  aggregates,  crystal  only  in  granular  limestone. 

H.  6.5;  Gr.  3.35-3.45.  Luster  vitreous  to  resinous.  Color 
brown,  green,  seldom  yellow  ;  colorless  by  transmitted  light, 
yellowish,  reddish,  seldom  brown.  Subtransparent  to  sub- 
translucent.  Comp.  a  basic  Ca-Al-silicate. 

Bp.  Fusible  at  3  with  intumescence  to  a  greenish  brown- 
ish glass ;  Fe  with  fluxes.  Chem.  Partly  decomposed  by 
HC1  and  completely  after  ignition.  Occurs  principally  in 
metamorphic  rocks  ;  most  common  in  limestones  and  silicate- 
hornstones  in  contact  formations,  less  common  in  gneiss . 

56.  Topaz.     Orthorhombic,  crystal,  rarely  in  grains  or 
masses. 

H.  8  ;  0^3.4-3.65.  Luster  vitreous.  Color  yellowish, 
white,  grayish,  greenish,  bluish,  reddish.  Transparent  to 
subtranslucent.  Comp.  5(Al3)SiO5  +  (Al,)SiF10. 

Bp.  Infusible ;  in  closed  tube  with  previously  fused  micro- 
cosmic  salt  fuses  and  etches  the  glass  for  HF;  blue  on  heat- 
ing with  cobalt  solution.  Chem.  Partly  attacked  by  HSO. 
Occurs  in  talc  and  mica-schists,  tin-bearing  granites  and 
greisen.  Alters  to  muscovite,  steatite,  kaolin. 

57.  Andalusite  (Chiastolite).    Orthorhombic,  always  crys- 
tal, seldom  in  grains,  never  massive. 

H.  7.5;  Gr.  3.16-3.20.  Luster  vitreous,  often  weak. 
Color  red,  gray,  brown,  green ;  by  transmitted  light  usually 
colorless.  Transparent  to  opaque,  usually  subtranslucent. 
Comp/Al2SiO5. 

Bp.  Infus.;  gives  blue  (Al)  on  heating  with  cobalt 
solution.  Chem.  Undecomposed  by  acids,  but  decomposed 
by  fusion  with  caustic  alkalies  and  carbonates.  Occurs  in 


SO  MANUAL    OF  LITHOLOGY. 

metamorphic  rocks  and  some  contact  formations;  some 
forms  are  like  sillimanite,  and  can  only  be  distinguished  by 
optical  differences.  Alters  to  mica,  cyanite,  kaolin. 

58.  Sillimanite  (Fibrolite).     Orthorhombic,  long  thin  pris- 
matic crystals.  , 

H.  6-7 ;  Gr.  3.25-3.34.  Luster  vitreous.  Color  brown, 
green,  grayish  white.  Transparent  to  translucent.  Comp.. 
like  andalusite  ;  also  bp.  Occurs  in  gneiss,  mica-schist,  and 
related  crystalline  rocks. 

59.  Cyanite  (Disthene).     Triclinic,  columnar  and  parallel 
aggregates. 

H.  5-7.25;  Gr.  3.56-3.67  (the  blue  varieties  are  heavier 
than  the  white).  Luster  vitreous  to  pearly.  Color  white, 
blue  (blue  along  the  center  of  the  blades  and  white  on 
margins.  Transparent  to  translucent.  Comp.  and  bp.  like 
last  two.  At  high  temperatures  in  the  furnace  is  altered  to 
sillimanite.  Occurs  in  metamorphic  and  crystalline  schists, 
almost  universally  with  garnet.  Alters  to  talc  and  steatite. 

60.  Tourmaline.     Hemimorphic,  rhombohedral,  colum- 
nar crystal,  rarely  granular-massive. 

H.  7-7.5  ;  Gr.  2.98-3.20.  Some  varieties  pyro-electric. 
Luster  vitreous  to  resinous.  Color  black,  blue,  green,  never 
white  or  colorless  as  a  rock-former ;  by  transmitted  light 
always  colored.  Transparent  to  opaque.  Comp.  a  silicate 
of  Al,  Bo,  and  either  Fe,  Mg,  Na,  or  K. 

Bp.  Variously  fusible,  those  with  Mg  easily  so  to  a 
white  blebby  glass  ;  with  increase  of  Fe  less  easily  so,  and 
to  a  slag  that  darkens  with  the  increased  percentage  of  Fe ; 
lithia  varieties  infusible;  some  react  for  Fe  and  Mn;  give 
boric  acid  with  bisulphate  of  potash  and  fluorite.  Chem. 
Not  decomposed  by  acids  till  after  fusion,  and  then  by 
HaSO4,  and  gelatinizes  with  HC1.  Occurs  in  older  granular 
and  acid  eruptives,  rarely  in  later  eruptives ;  alters  to  lepid- 
olite,  steatite,  etc. 


ROCK-FORMING   MINERAL^.  5 1 

61.  Staurolite.     Orthorhombic,    cruciform    twins,   pris- 
matic crystals. 

H.  7-7.5  ;  Gr.  3.66-3.75.  Luster  subvitreous  to  resinous. 
Color  shades  on  brown  and  black  ;  by  transmitted  light  yel- 
lowish-brown. Translucent-opaque.  Comp.  HFeAl5Si2O13. 

Bp.  Infusible  (Mg  varieties  fuse  easily  to  black  magnetic 
glass) ;  reacts  for  Fe  and  sometimes  Mn.  Chem.  Imper- 
fectly decomposed  by  H2SO4 ;  perfectly  so  by  HF.  Occurs 
in  crystalline  schists  and  in  contact  formations,  never  in 
eruptives.  Alters  to  steatite. 

PHOSPHATE. 

62.  Monazite.     Monoclinic,  small  crystals. 

H.  5-5.5  ;  Gr.  4.9-5.3.  Luster  resinous.  Color  shades  of 
red  and  brown.  Subtransparent  to  subtranslucent.  Comp. 
(Ce,La,Di)PO4,  with  some  Th.  Bp.  Infusible,  turns  gray 
and  gives  bluish-green  color  to  the  flame  when  moistened 
with  HSO  ;  with  borax  gives  a  bead  yellow  when  hot  and 
colorless  when  cool.  Chem.  Soluble  with  difficulty  in  HC1 
with  white  residue.  Abundant  in  gneiss  in  Brazil,  North 
Carolina  ;  in  large  crystals  in  pegmatite  dikes  in  Scandinavia 
and  Finland. 

OXIDES. 

63.  Corundum.     Rhombohedral,  also  massive  and  gran- 
ular. 

H.  9;  Gr.  3.9-4.16.  Luster  vitreous,  sometimes  pearly 
on  basal  planes  ;  and  sometimes  showing  a  six-rayed  opales- 
cent star  in  the  direction  of  the  axis.  Color  black,  blue,  red, 
yellow,  brown,  gray,  and  nearly  white.  Streak  uncolored. 
Transparent-translucent.  Fracture  conchoidal  to  uneven 
anu  splintery.  When  compact  exceedingly  tough.  Comp. 
A12O3.  Occurs  in  three  principal  varieties : 

(a)  Sapphire,   which  is  the   general   name   for   all   pure 


$2  MANUAL    OF  LITHOLOGY. 

transparent  to  translucent  states  which  are  valuable  as  gems, 
and,  according  to  color,  are  called  red  (true  of  oriental 
rub}7),  yellow  (oriental  topaz),  green  (oriental  emerald), 
purple  (oriental  amethyst). 

(ft)  Corundum,  which  includes  the  non-transparent  and 
dark-  or  dull-colored  states.  It  is  ground  and  used  as  an 
abrasive  and  polisher. 

(c)  Emery,  which  includes  the  granular  states  of  corun- 
dum which  are  black  or  dark-colored.  It  is  an  impure 
variety,  as  it  is  intimately  mixed  with  magnetite  and  hema- 
tite, and  is  used  for  the  same  purposes  as  the  last. 

Bp.  Unaltered ;  slowly  dissolves  in  borax  and  salt  of 
phosphorus  to  a  clear  glass,  which  is  colorless  when  free 
from  iron,  but  not  changed  by  fusion  with  soda  ;  a  fine  blue 
is  given  to  the  fine  powder  by  heating  with  cobalt  solution. 
Chem.  Insoluble  in  acids;  after  fusion  with  potassium  bi- 
sulphate  or  the  similar  soda  salt  is  soluble,  associated  with 
metamorphic  crystalline  rocks,  as  crystalline  limestones  and 
schists,  metagranite,  etc.  It  is  electric  by  friction. 

64.  Magnetite.  Isometric,  commonly  in  the  octahedron 
and  dodecahedron;  one  of  the  first-formed  minerals  in  rocks. 

H.  5.5-6.5 ;  Gr.  4.9-5.2.  Luster  metallic-submetallic. 
Color  iron-black.  Streak  black,  except  in  some  ores  that 
are  probably  mixtures  with  hematite,  and  where  there  is  the 
magnetic  reaction  with  a  more  or  less  reddish  streak. 
Opaque  when  in  mass,  but  subtransparent  when  in  folia  of 
mica.  Fracture  subconchoidal.  Brittle.  Strongly  mag- 
netic ;  separated  from  pulverized  rock  mass  by  a  weak 
magnet. 

Bp.  Fus.  with  diff.;  in  O.F.  becomes  non-magnetic;  with 
fluxes  is  like  hematite.  Chem.  Untouched  by  HF;  easily  sol. 
in  HC1.  As  a  rock  it  seems  to  be  a  varying  mixture  of 
protoxides  and  sesquioxides  of  iron,  and  its  color  and  streak 
vary  accordingly. 


ROCK-FORMING   MINERALS.  53 

Weathering.  Shows  crust  of  earthy  limonite  with  color 
yellowish  brown. 

It  is  the  most  widely  distributed  mineral  in  rocks,  but 
occurs  generally  in  small  proportion  and  so  minute  as  to  be 
detected  only  by  the  magnet  in  rock  powder ;  as  an  ore  it 
exists  in  lenticular  beds. 

65.  Chromite.    Isometric,  in  octahedrons,  generally  mass- 
ive. 

H.  5.5  ;  Gr.  4.32-4.8.  Luster  submetallic.  Streak  brown. 
Iron-black  to  brownish  black;  by  transmitted  light  gray, 
lilac-gray.  Opaque  in  mass.  Fracture  uneven.  Brittle. 
Sometimes  magnetic. 

Bp.  Inf.  in  O.F.;  slightly  rounded  on  edges  in  R.F.  and 
becomes  magnetic ;  with  fluxes  shows  iron  reaction  when 
hot,  but  chrome-green  when  cold.  Chem.  Slightly  touched 
by  acids,  but  decomposed  after  fusion  with  alkali  bisul- 
phates. 

Occurs  in  serpentine  and  in  meteorites;  never  as  an  es- 
sential component  of  rocks. 

CARBONATES. 

66.  Calcite.  Rhombohedral,  never  in  crystals;  in  irregular 
grains  and  plates. 

H.  3  ;  Gr.  2.71.  Luster  vitreous,  subvitreous,  resinous. 
Color  white  and  variously  colored.  Transparent-opaque. 
Comp.  CaCO3. 

Bp.  Infus.  and  glows  with  reddish-yellow  flame.  Chem. 
Effervesces  with  cold  HC1. 

Occurs  most  extensively,  after  quartz,  of  all  the  minerals, 
as  limestones,  which  will  be  treated  later ;  also  occurs  in 
basic  rocks  as  a  filling  of  cracks,  cavities,  and  amygdaloidal 
openings,  and  replaces  silicates  with  pseudomorphs  after 
them  ;  also  infiltrates  from  the  country  rocks  of  the  mass. 
When  limestone  is  metamorphosed  it  becomes  "  marble." 


54  MANUAL    OF  LITHOLOGY. 

67.  Dolomite.  Rhombohedral,  crystals  saccharoidal  with 
curved  faces,  grains. 

H.  3.5-4 ;  Gr.  2.8-2.9.  Luster  vitreo-pearly.  Color  white 
to  black  through  reds,  browns,  greens,  and  grays.  Trans- 
parent to  translucent.  Comp.  (Ca,Mg)CO3. 

Bp.  Generally  like  calcite,  but  does  not,  like  it,  give  a 
clear  mass  with  soda  on  platinum  foil.  Chem.  Cold  HC1 
acts  slowly  on  fragments. 

It  occurs  in  sedimentary  strata,  which  are  sometimes 
altered  from  limestone  through  Mg  solutions ;  also  occurs 
locally  in  metamorphosed  clay  slates  and  phyllites ;  more 
frequently  associated  with  magnesia  rocks  and  minerals  than 
calcite. 

(The  other  minerals  occurring  as  rocks  will  be  treated 
later  as  economic  products.) 

The  following  are  decomposition  products: 

Viridite  is  a  greenish  translucent  form  of  matter  in  minute 
scales  and  fibres,  which  results  from  the  decomposition  of 
hornblende,  pyroxene,  and  olivine. 

Ferrite.  Amorphous  yellow,  brown,  or  red  earthy  matter, 
frequently  pseudomorphous  after  minerals  containing  iron. 
Chemically  it  is  anhydrous  or  hydrated  sesquioxide  of  'iron, 
and  forms  the  coloring  matter  of  porphyries  and  weathered 
porphyrites. 

Opacite.  A  term  applied  to  black  opaque  amorphous 
matter  in  granules,  patches,  or  scales,  which  occurs  in  rocks 
containing  magnetite,  and  which  some  authorities  state  to 
be  composed  of  it. 


GENERAL  DEFINITIONS. 

Minerals  occur  in  rocks  in  various  (M)  forms,  as  shown 
in  the  preceding  pages.  From  them  we  see  that  two  general 
forms  occur  in  mineral  matter  —  individualized,  when  it  is 
bounded  by  surfaces  that  can  be  readily  distinguished  (M) 
or  (;«),  and  unindividualized,  when  it  forms  an  amorphous 
mass  or  occurs  in  patches  between  individualized  matter. 

Individualized  forms  are  : 

(a)  More  or  less  perfect  crystals,  the  failure  in  perfecting 
the   shape   being   due  to  want  of  material  or  stoppage  of 
crystallization,    rather    than    to    interference    from    other 
forces,  as  : 

1.  Perfect  crystals  with  regular  terminations. 

2.  Prismatic  shapes  with  unterminated  ends,  which  may 
be  solid,  fibrous,  lath-shaped,  columnar,  or  a  mere  shell  filled 
with  other  minerals. 

3.  Solid  pyramidal  heads  with  prismatic  faces  mo?e  or 
less  complete,  or  merely  sketched  by  a  few  fibres,  like  the 
teeth  of  a  comb. 

4.  What  may  be  styled  the  unterminated  skeletons  of 
crystals,   with  only  portions  of  the  prismatic  faces  devel- 
oped in  irregular  patches,  and  of  the  most  minute  thinness, 
which  disappear  entirely  in  places  and  leave  only  a  tendency 
to   break   from   the  enclosing   body  along  those  (missing) 
faces. 

(b)  Crystalline  grains  which  have  an  internal  crystalloid 
structure  (as  shown  by  polarized  light),  but  whose   exterior 
presents  irregular  shapes  due  to  interferences  in  crystalliza- 
tion, or  to  fracture  or  abrasion. 

55 


$6  MANUAL   OF  LITHOLOGY.\ 

Unindividualized  forms  are : 

(a)  Vitreous  particles  or  masses  due  to  fusion  and  sudden 
cooling. 

(b)  Colloid  masses,  lithoid,  stony. 

(c)  Aggregations  of  indefinite  form,  belonging  to  none  of 
the  above,  and  occurring  in  streaks,  stains,  tufts,  etc. 

Lithologyvn  a  megascopic  basis  requires  that  classifications 
and  definitions  conform  closely  to  observations  with  the  eye 
and  lens ;  and  the  microscope  must  be  left  for  theories  of 
rock-formation.  In  the  following  pages  association  in  nature 
(geological),  mineral  and  physical  states  will  be  employed  in 
forming  divisions  and  groups,  and  bulk  analyses  used  only  as 
checks.  The  physical  states  are  used  in  definitions  of  texture 
and  structure. 

TEXTURE. 

This  refers  to  the  size,  shape,  state,  and  mode  of  union  of 
the  individual  particles  of  a  rock,  whether  they  be  single 
minerals,  aggregates  of  minerals,  or  fragments  of  an  older 
rock.  In  each  case  the  texture  definition  must  give  the  ex- 
ternal and  internal  condition  of  those  particles.  These  con- 
ditions are  characteristic  or  irregular.  The  former  are  pecul- 
iar to  free  crystallization  in  a  saturated  solution ;  the  latter 
to  any  other  mode  of  formation,  as  (a)  crystallization  under 
other  conditions  than  those  above  given,  or  (b)  to  organic 
or  other  mode  of  aggregation. 

The  divisions  of  texture  are  : 

(A)  When  some  (hypophaneromeric)  or  <z//0/"(phaneromeric) 
the  particles  can  be  distinguished  by  the  eye  or  the  lens.  The 
varieties  are  : 

1.  Crystal,  when  both  internal  and  external  arrangement 
are  characteristic.  This  is  the  "  automorph  "  of  Rohrbach, 
and  the  "  idiomorph  "  of  Rosenbusch.  The  latter,  though 
the  later,  term  is  the  better,  as  it  means  "  characteristic," 
while  the  former  is  "  natural."  The  converse  of  this  is  the 


GENERAL   DEFINITIONS.  57 

"  xenomorph  "  of  Rohrbach,  and  u  allotriomorph"  of  Rosen- 
busch,  and  here  the  latter  term  is  again  the  better,  as  the 
former  is  ''foreign,"  while  the  latter  is  "peculiar  to  an- 
other," and  the  crystallization  of  many  minerals  simultan- 
eously imposes  on  each  forms  peculiar  to  the  bounding 
planes  of  those  adjacent.  Rocks  cannot  be  formed  wholly 
of  crystals,  and  the  term  "  holocrystalline  "  of  Rosenbusch 
means  "  wholly  crystalline-granular,"  and  will  be  so  used 
hereafter;  but  it  might  be  forced  from  this  sense  to  mean 
"  wholly  crystal  (M\"  where  a  rock  has  sufficient  base  to 
form  an  exceedingly  fine-grained  porphyry  of  its  ground- 
mass.  There  must,  therefore,  be  a  cementing  medium  when 
minerals  occur  crystal,  and  they  so  occur  in  three  forms  : 

(a)  Individual  crystals  ("  phenocrysts  "  of  Iddings),  or  frag- 
ments of  crystals  scattered  through  a  groundmass  to  form 
a  porphyroid  texture  or  a  porphyry.  According  to  J.  D.  Dana 
the  rock  is  "  quartzophyric,"  "  plagiophyric,"  "  leucito- 
phyric,"  etc,  as  the  phenocrysts  are  quartz,  etc.  The  ground- 
mass  may  be  divided  (Iddings)  into : 

1.  Anisotropic,  or  not  of  uniform  constitution,  when  it  is  a 
holocrystalline   mixture    with   particles   of   different   sizes, 
which  is  Vogelsang's granophyre  (if  microscopic) ;    or  a  mix- 
ture of  phenocrysts  in  an  isotropic  base. 

2.  Isotropic,  or  the  reverse  of  the  former,  when  the  micro- 
scope shows  only  amorphous  matter,  which  is  Vogelsang's 
felsophyre  (when  felsitic)  and  vitrophyre  (when  glass;. 

The  late  Dr.  G.  H.  Williams  divides  the  holocrystalline 
groundmass  into  one  : 

(a)  Wholly  composed  of  individual  crystalline  grains,  or 
microgran  itic. 

(ft]  Where  two  minerals  crystallized  simultaneously  and 
with  equal  rapidity,  so  that  they  became  equidimensional 
and  mutually  interpenetrant,  or  micropegmatitic  (see  "  Impli- 
cation Structure"). 


$8  MANUAL   OF  LITHOLOGY. 

(y)  Where  a  single  large  crystal  or  one  of  the  two  com- 
ponents of  the  groundmass  may  be  filled  with  smaller  and 
irregular  grains  or  crystals  of  the  latter,  he  suggests  the 
term poikilitic,  and,  when  microscopic,  micropoikilitic. 

Rosenbusch  calls  all  crystals  formed  in  the  fluid  magma 
in  the  hot  abysses  intratelluric,  and  many  authorities  state 
that  the  porphyroid  texture  is  peculiar  to  such  a  crystal- 
lization, while  Judd,  Van  Hise,  and  others  have  shown  that 
some  have  been  caused  by  secondary  growths  about  crys- 
tals after  solidification. 

(/>)  As  phenocrysts  distributed  through  a  crystalline- 
granular  foliated  mass,  as  in  the  metamorphic  schists,  to  form 
porphyritic  states  of  those  rocks. 

(c)  As  the  result  of  "  crystallinic  metamorphism  "  (J.  D. 
Dana),  where  crystals  have  been  built  up  by  infiltrating  so- 
lutions, as  just  described. 

II.  Granular,  when  either  internal  or  external  arrange- 
ment, or  both,  are  not  characteristic.  We  can  distinguish 
two  varieties  of  internal  arrangement — characteristic,  or  crys- 
talloid, as  in  crystals  (and  apparent  by  polarized  light),  and 
amorphous,  as  in  organic  formations ;  guano,  shells,  etc. 

We  can  also  distinguish  three  varieties  in  external  form  : 

(a)  Crystalline,  where  the  internal  arrangement  is  crystal- 
loid, but  the  external  form  is  irregular,  owing  to  an  inter- 
ference in  the  crystallizing  of  the  components  through  their 
mutually  constricting  the  areas  in  which  they  formed,  as 
where  crystallization  is  simultaneous  in  a  solution  of  two  or 
more  minerals,  and  the  particles  are  bounded  by  irregular 
and  few  faces  whose  shapes  depend,  not  on  the  character 
of  the  mineral,  but  on  the  shape  of  the  area  in  which  it 
formed.  This  variety  is  found  in  massive  and  highly  meta- 
morphic rocks,  and  is  usually  preceded  by  an  adjective  to 
give  the  size  of  the  components,  as  phanerocrystalline,  where 
they  can  be  detected  by  the  eye,  and  cryptocrystalline,  when 


GENERAL   DEFINITIONS.  59 

th^y  cannot  be  resolved  even  by  the  highest  power  of  the 
microscope,  but  where  the  glistening  of  the  minute  cleav- 
age faces  in  incident  light  shows  a  crystalline  texture. 
Under  phanerocrystalline  we  distinguish  coarse-,  medium-, 
fine-,  and  micro-crystalline.  The  last  cannot  be  resolved  by 
the  lens,  but  exhibits  the  glistening  noted  under  crypto- 
crystalline.  Medium-crystalline  is  so  peculiar  to  granites 
that  it  called  granitoid,  and,  if  the  rock  is  drusy,  miarolitic. 
The  form  of  crystalline  grains  can  be  readily  seen  by  wash- 
ing a  thoroughly  kaolinized  granite  till  the  quartz  is  clean. 
As  quartz  is  the  last  to  crystallize  in  granite,  it  is  forced  to 
.accommodate  itself  to  the  interstices  between  the  already 
formed  feldspar  and  mica,  and  most  highly  shows  the  pe- 
culiar outline  called  "  crystalline."  Holocrystalline  rocks, 
therefore,  have  their  components  crystallized  into  one  an- 
other without  the  aid  of  a  cementing  medium. 

(b]  Clastic  (Greek,  "  broken  in  pieces"),  where  the  inter- 
nal arrangement  of  the  particles  may  be  crystalloid  or  amor- 
phous, but  where  the  external  form  —  whether  in  indi- 
vidual minerals  or  pieces  of  older  rocks  —  is  produced  by 
fractured  surfaces,  or  by  faces  (crystal  or  irregular)  more 
•or  less  worn  by  mechanical  or  chemical  agents.  Naumann 
called  classes  larger  than  a  hazel  nut  psephites,  sand  sizes, 
J>sammites,  and  slime  sizes,  pelites.  Clastics  are  always 
secondary  and  derivative,  and  their  components  may  have 
an  angular  or  a  rounded  outline  —  the  former  being  the  result 
•of  fracture  ;  the  latter,  the  modified  form  after  transporta- 
tion and  weathering.  Angular  particles  are  called  sharp,  as 
a  "sharp  sand,"  which,  when  solidified,  forms  a  rock  of 
rough  feel  and  is  called  a  grit.  Angular  particles  become 
rounded  by  mechanical  agents,  as  moving  water  (rolled) 
or  moving  ice  (glaciated) ;  by  chemical  agents  in  weather- 
ing (etched).  On  breaking  elastics  there  is  not  that  showing 
of  cleavage  faces  as  in  crystalline  rocks,  —  even  if  the  grains 


60  MANUAL    OF  LITHOLOGY. 

are  crystalloid,  —  as  the  particles  are  not  crystallized  into 
one  another.  They  are,  on  the  contrary,  more  or  less 
dull  on  the  surface,  and  are  cemented  together  so  loosely 
that  the  fracture  extends  around  the  particles  instead  of  across 
them,  and  the  surface  exhibits  only  the  combined  dull  surfaces 
of  the  particles  in  a  very  characteristic  manner.  When  the 
cementing  medium  is  of  the  same  mineral  as  the  rock,  incip- 
ient metamorphism  may  produce  something  like  the  crys- 
talline fracture.  Similar  comparatives  are  prefixed  to  clastic 
as  to  crystalline  to  denote  the  sizes  of  the  grains — microclas- 
tic,  for  example.  "  Pyroclastic  "  is  applied  to  fragments  of 
the  walls  of  dikes  or  volcanic  vents  which  have  been  broken 
by  the  earth-throes,  or  by  the  abrasion  of  the  intruding  fluid. 
Psephites  are  called  agglomerates  when  the  fragments  are 
huge  and  heaped  together  disorderly,  as  by  the  caving  in 
of  the  top  of  a  cavern  in  a  limestone  formation,  or  the  filling 
of  the  vent  of  a  volcano  by  the  fallen  sides ;  breccias  when 
all  the  fragments  are  angular.  Through  variations  in  the 
cementing  medium  we  distinguish  pyroclastic-breccias,  where 
fragments  of  the  country  rock  have  been  cemented  by  the 
erupted  mass ;  oroclastic-breccias,  where  the  grinding  of  the 
walls  of  the  fissure  on  one  another  has  filled  it  with  their 
fragments,  which  have  been  cemented  by  intruding  so- 
lutions of  vein  material;  or,  as  in  the  Siluro-Cambrian  lime- 
stone of  eastern  Pennsylvania,  orogenic  forces  have  exten- 
sively crushed  the  formation,  but  not  displaced  it,  and  in- 
filtrating waters  have  cemented  its  fragments  in  almost  their 
original  positions.  To  this  formation  the  term  brecciated  is 
applied,  and  ordinary  breccias,  where  cliffs  have  scaled  from 
aerial  changes,  and  their  fragments  have  been  cemented. 
When  the  fragments  are  a  mixture  of  angular  and  rolled 
shapes,  it  is  called  brecciated  conglomerate,  and  when  entirely 
rolled,  a  conglomerate.  If  some  rolled  portions  of  greater  size 
than  the  average  are  scattered  through  the  mass,  the  rock 


GENERAL   DEFINITIONS.  6 1 

becomes  a  pudding-stone.  These  terms  alone  do  not  form  suf- 
ficient distinction  for  rocks,  so  that  we  must  call  them  after 
the  rocks  from  which  they  originated,  as  "  quartz-breccia," 
"  quartz-conglomerate,"  "  diorite-conglomerate,"  "  clay-slate- 
diorite-breccia."  Very  coarse  conglomerate  is  called  shingle 
when  the  fragments  are  larger  than  a  man's  fist,  and  have 
been  formed  by  the  grinding  action  of  water  on  hard 
crystalline  rocks.  There  is  a  class  of  formations  that  in- 
cludes all  sizes  from  the  finest  silt  to  blocks  as  large  as  a 
house,  and  which  occur  in  generally  unstratified  aggregates, 
to  form  till,  moraine-stuff,  bowlder-clay,  etc.  These  are  due 
to  glaciers  with  or  without  the  concurrent  action  of  moving 
water,  and  will  be  more  fully  defined  later.  The  varieties 
of  psam mites  and  pelites  will  be  similarly  explained. 

(c)  Irregular,  where  both  internal  and  external  arrange- 
ment are  amorphous,  as  in  peat,  guano,  and  similar  rocks  of 
organic  origin.  The  phosphate  rocks  may  consist  of  coral- 
line limestones  underlying  guano  beds,  and  into  which  the 
aerial  waters  have  carried  the  soluble  portions  of  the  guano. 
This  metachemized  rock  is  also  called  "  guano."  Or,  in  the 
Tertiary  aggregates  of  bones  of  land  and  marine  animals, 
common  to  the  coast  regions  of  the  southern  Atlantic  States, 
we  have  a  peculiar  formation,  also  found  in  the  floor  de- 
posits of  some  caverns,  and  called  bone-breccia. 

(R)  Cryptomeric,  when  none  of  the  particles  can  be  distin- 
guished. There  are  two  varieties  of  this : 

i.  When  they  are  fused  together  in  an  amorphous  mass; 
it  is  vitreous  or  glassy,  when  it  has  a  texture  and  luster  like 
.glass,  as  in  obsidian ;  resinous,  when,  with  similar  texture, 
the  luster  is  like  resin,  as  in  pitchstone ;  horny,  flinty,  when 
homogeneous,  cryptocrystalline,  and  with  waxy  luster,  as  in 
jasper  and  flint ;  lithoidor  stony,  with  similar  texture  and  want- 
ing luster.  This  commonly  is  the  result  of  "  devitrification/* 
or  the  conversion  of  a  vitreous  into  a  crystalline  texture. 


62  MANUAL    OF  LITHOLOGY. 

2.  When  they  adhere  loosely  without  fusion,  it  is  com- 
pact, when  dull,  firm,  and  homogeneous ;  earthy,  when  com- 
posed of  loose,  friable  particles ;  plastic,  common  to  the 
pelites,  capable  of  being  moulded,  formed,  or  modelled ; 
pulverulent,  when  the  compound  is  so  fine  and  loosely  ce- 
mented that  it  can  be  converted  to  dust  by  pressing  between 
the  fingers ;  incoherent,  when  it  is  still  more  loosely  held  to- 
gether, and  loses  its  shape  by  a  slight  shock  or  a  puff  of  air. 

Devitrification.  This  is  a  changing  of  a  vitreous  to  a 
crystalline  texture  by  means  not  well  known.  It  is  seen  in 
the  case  of  pitchstone  dikes  whose  centres  are  glass  while 
the  selvages  are  quartz-porphyry.  The  felsites  of  Wales  are 
shown  to  be  pitchstones  devitrified  on  an  enormous  scale, 
and  similar  widespread  changes  have  taken  place  in  the 
ancient  rhyolites  of  the  South  Mountain  on  the  borders  of 
Pennsylvania  and  Maryland.  Devitrification  is  shown  by 
the  formation  of  microliths,  crystalline  granules,  or  crystals 
which  finally  produce  felsitic  textures,  so  that  the  fluxion 
structures,  lithophysae,  etc.,  are  all  that  remain  to  testify  to 
its  original  state.  Some  authorities  go  so  far  as  to  say  that 
the  quartz-porphyries,  felsites,  etc.,  are  only  devitrified  forms 
of  old  extrusive  glasses. 

STRUCTURE. 

This  refers  to  the  form — external  or  internal — in  which 
the  rock  is  massed.  Internal  structure  generally  has  no- 
effect  on  the  external  shape.  Some  structures  can  be  seen 
only  in  terranes,  others  are  exhibited  in  hand  specimens, 
while  a  third  class  are  revealed  only  by  the  microscope. 
Before  describing  them  some  of  their  causes  will  be  briefly 
outlined,  such  as  pressure,  cooling,  drying,  solution,  weather- 
ing,  sedimentation,  abrasion,  impregnation,  secretion,  and 
convergence. 


GENERAL   DEFINITIONS.  63 

Causes  of  Structural  Variations. 

Pressure.  The  effects  of  pressure  depend  on  whether  it 
be  applied  to  a  homogeneous  and  equally  resisting  mass,  or 
to  one  with  portions  varying  in  resistance  to  deformation, 
whether  the  mass  be  plastic  or  solid,  and  whether  the  mass 
may  be  displaced  as  a  whole  by  the  pressure  or  not.  Tyn- 
dall  has  shown  that  pressure  applied  to  a  homogeneous 
mass  without  power  of  motion  along  the  direction  of  the 
force  will  produce  a  tendency  to  split  into  parallel  plates 
whose  planes  are  at  right  angles  to  the  direction  of  pressure. 
These  planes  are  called  cleavage-planes  in  fine-grained  masses, 
and  some  varieties  of  foliations  result  in  coarser  masses  from 
the  same  source.  In  case  the  mass  be  solid  and  the  pressure 
produces  a  warping  or  torsion,  a  series  of  fractures  relatively 
parallel  to  one  another  occur,  and  these  are  crossed  by  a 
second  series  making  slight  variations  from  a  right  angle 
with  the  first  set.  These  are  joints.  With  unequal  resistance 
to  deformation  certain  portions  of  the  mass  move  through 
greater  distances  than  adjacent  portions,  and  shears  result. 
The  fractures  thus  formed  may  be  slight  or  of  vast  di- 
mensions. In  a  sedimentary  mass  the  gradual  weighting  of 
the  overlying  portions  exerts  an  increasing  pressure  on  the 
lower  parts,  and  if  these  are  locally  of  varying  degrees  of 
resistance,  the  stronger  parts  will  retain  their  form  and  pro- 
ject into  the  softer  overlying  parts,  that  sink  around  them, 
as  shown  by  Marsh  in  the  case  of  stylolites.  With  a  greater 
solidity  to  the  mass  the  grinding  of  the  sides  of  the  fracture 
on  each  other  will  produce  groovings  and  polishing.  In  the 
gneiss  of  the  South  Mountain,  in  Pennsylvania,  an  abundance 
of  minute  slickensides  occur  from  this  cause  where  the  rela- 
tive area  of  fracture  is  but  a  few  square  inches.  Pressure 
applied  to  the  edges  of  a  mass  that  has  freedom  for  bending 
wrill  produce  two  series  of  fractures  at  right  angles  to  one 


64  MANUAL    OF  LITHOLOGY. 

another.  The  first  series  are  parallel  to  the  axis  of  the 
cylinder  or  cylindroid  formed  by  the  mass,  and  radial,  and 
are  caused  by  the  stretching  of  the  upper  layers  of  the  mass. 
The  second  series  are  caused  by  inequality  in  resistance  to 
the  pressure,  as  above  stated,  and  the  shears  produce 
fractures  parallel  to  the  direction  of  pressure.  The  latter  is 
the  ordinary  cause  vi  faults,  with  extensive  movement  of  the 
walls  up  and  down,  as  shown  in  slickensides  of  great  areas. 
The  two  series  of  fractures  can  be  beautifully  seen  in  the 
hard  slate  partings  of  the  sharply  flexed  beds  of  anthracite 
in  this  State. 

Cooling.  On  cooling  a  molten  mass  against  a  plane  sur- 
face strains  are  developed  that  cause  symmetrical  fractures 
to  extend  normal  to  that  surface,  and  divide  the  mass  into 
prisms  with  polygonal  section.  In  a  dike  the  walls  are 
cooling  surfaces,  and  the  prisms  run  across  the  dike-open- 
ing ;  in  a  surface  sheet  the  prisms  are  vertical ;  in  either  case 
the  axis  of  the  prisms  is  normal  to  the  plane  of  flow.  Owing 
to  the  quicker  cooling  of  the  part  near  the  walls,  secondary 
fractures  are  caused  parallel  to  them,  so  that  the  prisms  are 
divided  by  planes  parallel  to  the  base.  (See  further  under 
"Weathering.") 

Drying.  In  sands  and  muds  a  variety  of  structures  are 
produced  by  surface  and  internal  drying.  Surface  drying 
produces  two  series  of  cracks  at  right  angles  to  one  another. 
The  former  are  due  to  the  shrinkage  of  the  mass,  and  extend 
into  it  normally  to  the  drying  surface,  as  can  be  seen  in  any 
mud  flat  exposed  to  the  sun  and  air,  in  the  form  of  polygonal 
prisms,  much  like  those  caused  by  cooling,  but  irregular  in 
outline ;  the  latter  are  due  to  the  more  rapid  drying  of  the 
upper  layer  of  the  mass,  and  a  corresponding  shear,  that 
separates  that  layer  from  the  next  and  causes  it  to  curl  up- 
wards where  this  fracture  meets  the  prisms.  This  latter 
form  is  seen  in  the  greater  readiness  of  masses  of  plaster  of 
Paris  or  artificial  stone  solidified  in  uncovered  boxes  to 


GENERAL   DEFINITIOA^S.  65 

fracture  parallel  to  the  drying  surface  more  readily  than 
across  it. 

Internal  drying  takes  place  in  pelitic  masses  that  are  ex- 
posed  to  loss  of  moisture  on  several  sides.  The  exterior  on 
drying  becomes  rigid,  and  the  moisture  of  the  interior  passes 
through  it  without  influencing  the  shape ;  but  the  loss  of 
moisture  makes  the  enclosed  portion  shrink  away  from  the 
dry  shell.  The  new  surface  of  the  latter  may  dry  in  a  similar 
manner,  and  have  a  second  shell  formed.  The  so-called 
"  rattle-stones  "  in  clay  are  formed  in  this  way.  A  second 
type  of  centripetal  drying  forms  the  concentric  rings  of 
staining  (J.  D.  Dana)  seen  in  breaking  sedimentary  masses. 

Solution.  The  passage  of  waters  through  the  earth's 
crust,  with  or  without  acids  in  solution,  dissolves  portions 
of  the  crust  along  the  lines  of  flow,  and  etches  the  surfaces 
over  which  they  pass,  or  excavates  caverns  of  varying  di- 
mensions. Limestones  are  the  best  examples  of  rocks  thus 
affected,  and  the  great  caves  of  the  world  are  in  this  rock. 
(See  further  under  the  next  topic.) 

Weathering.  The  weathering  of  rocks  depends  on  their 
mineralogical  composition  and  mode  of  aggregation,  and 
comprises  those  changes  in  shape  and  character  due  to 
exposure  to  the  "  weather,"  i.e.,  to  the  atmospheric  agents, 
taken  in  their  most  extended  sense.  These  are  the  mechan- 
ical and  chemical  effects  of  the  air  (wind,  rain,  humidity, 
variations  in  temperature,  frost,  and  the  chemical  solvents) 
and  the  humic  forces  (mechanical  effects  of  growing  vegeta- 
tion and  the  acids  of  the  soil).  The  result  is  the  reduction 
of  solids  to  a  friable,  sectile,  or  plastic  state  by  the  removal 
of  soluble  ingredients  ;  or  the  formation  of  carbonates,  oxides, 
or  haloids.  Under  the  first  case  a  granite  becomes  a  crumbly 
mass  of  quartz  fragments  imbedded  in  kaolin,  which  may  be 
white,  or  stained  with  iron  from  whatever  ferruginous 
bisilicate  formed  the  essential  mineral ;  a  trachytic  porphyry 
kaolinizes  to  a  compact  and  sectile  tuff,  and  a  clay  slate 


66  MANUAL   OF  LITHOLOGY. 

turns  to  a  bed  of  clay.  Under  the  second  case  an  outcrop 
of  argentiferous  galena  changes  to  carbonate,  or  to  horn 
silver;  while  the  well  known  "  iron  hat"  forms  on  a  pyri- 
tiferous  lode.  A  rock  can  frequently  be  determined  by 
weathering  alone  when  there  is  a  great  and  well-marked 
difference  between  the  fresh  and  weathered  states — especially 
if  it  be  a  non-fossiliferous  part  of  a  generally  fossiliferous 
formation.  The  rolled  cobbles  of  Oriskany  sandstone  in 
eastern  Pennsylvania  take  a  high  polish  and  a  deep  red,  the 
latter  from  the  oxidation  of  the  minute  portions  of  iron  in 
the  mass,  which  give  the  fresh  rock  a  slight  tinge,  as  can  be 
seen  on  breaking  a  bowlder,  whose  interior  is  whitish  and 
gritty.  Ferruginous  rocks  highly  oxidized  on  the  surface 
are  bleached  when  covered  by  peat  bogs,  while,  on  the  con- 
trary, white  quartz  pebbles  are  deeply  and  irregularly  stained 
by  immersion  in  ferruginous  muds,  as  are  the  pebbles  of 
Potsdam  quartzite  in  Triassic  conglomerate  in  eastern  Penn- 
sylvania. A  limestone  that  appears  compact  and  non-fos- 
siliferous on  a  fresh  fracture  may  be  found  to  be  highly 
fossiliferous  if  we  examine  the  etched  fragments  in  the 
weathered  talus,  where  the  less  soluble  fossils  stand  in  high 
relief.  Weathering,  therefore,  affects  the  hardness,  color, 
and  composition  of  a  rock,  or  all  of  them,  and  the  student 
should  become  familiar  with  the  various  states.  Some  rocks 
are  exceptions  and  harden  on  weathering,  as  do  sinters,  some 
sandstones,  and  the  shell  aggregate  of  Florida,  called  coquina, 
owing  to  the  hardening  of  the  cementing  medium  through 
drying.  Weathering  acts  more  rapidly  along  than  across 
bedding  planes,  and  frequently  reveals  the  bedding  in  an 
apparently  unstratified  mass.  Weathering  also  shapes  masses 
by  removing  more  rapidly  the  sharp  angles,  and  reducing 
the  mass  to  a  spheroid  (spheroidal  weathering).  The  fracture 
of  a  spheroid  discloses  a  series  of  concentric  shells  that 
approximate  in  composition  from  the  fresh  nucleus  to  the 
highly  oxidized  exterior.  Spheroidal  weathering  also  takes 


GENERAL   DEFINITIONS.  6/ 

place  in  rocks  with  no  soluble  ingredients,  as  in  the  Potsdam 
quartzite  of  eastern  Pennsylvania.  Here  it  is  due  to  sudden 
alterations  in  temperature  from  rain-squalls  on  a  hot  day. 
The  effects  of  sudden  cooling  can  best  be  studied  on  the 
sea-shore  in  the  northern  part  of  the  temperate  zone  during" 
the  summer,  where  there  is  an  abundance  of  bowlders  of 
eruptive  rocks.  These  become  intensely  heated  during  low 
tide,  and  give  low  cracking  sounds  when  first  struck  by  the 
returning  waves.  Cold  showers  have  a  slighter  effect. 
This  is  accompanied  by  alteration  of  the  minerals  through 
the  changes  mentioned  above.  This  variety  of  weathering 
seems  to  be  greater  in  a  composition  of  highly  basic  aniso- 
metric  minerals,  owing,  perhaps,  to  the  inequality  of  strain 
in  the  heated  part,  and  the  sudden  and  unequal  contraction 
in  cooling,  which,  in  many  cases,  produces  flaking,  and  may 
be  the  cause  of  the  decay  of  the  Egyptian  obelisks  since 
their  removal  from  that  country,  as  they  remained  there 
intact  for  centuries,  whether  in  the  air,  or  half  buried  in  the 
bitter  brines  with  which  the  soil  is  saturated,  but  have 
deteriorated  when  removed  from  a  climate  of  uniform  tem- 
perature to  those  of  great  and  sudden  variation.  Joints, 
fractures,  cleavages,  and  bedding  planes  aid  weathering,  and 
the  depth  of  weathering  depends  on  the  relative  progress 
of  formation  and  removal  of  the  decomposed  part,  and  varies 
with  latitude  and  location.  Weathering,  finally,  is  a  variety 
of  metachemism. 

Sedimentation.  This  is  the  deposit  by  and  under  water  of 
the  worn  material  from  weathered  rocks.  If  the  deposition 
is  continuous  and  the  material  uniform  in  size,  there  will  be 
formed  a  mass  of  uniform  character  when  viewed  on  a  section 
made  in  any  direction.  Moving  water  has  a  sorting  power, 
and  Hopkins  has  shown  that  this  varies  with  the  sixth  power 
of  the  velocity.  During  the  spring  and  fall  freshets  the  rivers 
are  carrying  a  burden  of  larger  sizes  than  during  the  low 
waters  of  summer  and  winter.  Sediments  thus  formed  will 


68  MANUAL    OF  LITHOLOGY. 

show  coarser  and  finer  layers  intermixed.  Leconte  has 
.summed  the  conditions  for  this  intermixing  of  layers,  called 
stratification,  as  follows :  for  stratification  in  still  water  (a 
lake  or  the  ocean)  there  must  be  a  heterogeneous  supply  and 
an  intermittent  cause,  while  for  running  water  there  must  be 
in  addition  a  variable  current.  If  the  strata  are  formed  of 
different  compositions,  as  sand,  clay,  calcareous  mud,  etc.,  they 
are  called  beds  of  sand,  clay,  etc.  Sedimentary  formations 
are  called  bedded,  and  the  planes  or  surfaces  that  separate 
adjacent  beds  are  bedding  planes,  etc.  A  section  of  stratified 
rocks  generally  shows  a  variation  in  size,  kind,  or  color  of 
material,  or  all  of  them,  and  such  rocks  tend  to  split  more 
readily  along  than  across  the  bedding  planes,  while  penetrat- 
ing solutions  enter  more  easily  along  than  across  the  same, 
even  though  the  mass  be  fine  grained,  as  in  the  pelites,  and 
the  stratification  planes  are  not  apparent.  The  variations  in 
.structures  will  be  noted  later. 

Abrasion  is  a  rounding  of  the  surfaces  of  rocks  by  contact 
with  other  rocks  moved  by  air  or  water.  The  winds  carry 
fine  sands,  and  sculpture  and  polish  the  rock  faces  exposed 
to  their  action,  as  is  seen  in  the  Western  States,  in  Egypt,  and 
along  sea-coasts.  From  a  study  of  the  etched  windows  along 
the  New  Jersey  coast  the  "  sand-blast  "  was  devised,  by  which 
stones  of  any  hardness  are  cut  to  any  shape  required,  pierced, 
and  otherwise  worked.  The  prime  motor  in  abrasion  is  water, 
.liquid  or  frozen.  Rocks  in  river  bottoms  are  rounded  by 
nvhat  is  dragged  over  them.  Rapidly  moving  water  in  tor- 
Tents  or  waves  rolls  fragments  together  as  in  a  barrel  and 
rounds  them  by  mutual  attrition.  Glaciers  round  the  sur- 
iaces  of  hard  rocks  over  which  they  flow  and  form  "  sheep- 
tbacks,"  "  whale-backs,"  etc.,  while  the  fragments  that  do  the 
work  are  themselves  more  or  less  rounded.  Water-rounding 
by  strong  currents  is  called  rolling,  ice  action,  glaciation. 

Impregnation.     This  is  due  to  thermal  waters  or  vapors 


GENERAL   DEFINITIONS.  69 

acting  along  certain  planes  in  a  mass,  and  introducing  foreign 
elements  to  form  new  mineral  combinations.  The  first  case 
is  where  a  solid  porous  rock  is  fractured,  and  along  the  frac- 
ture comes  thermal  water  or  vapor  to  penetrate  the  pores 
for  a  limited  distance  from  the  fracture,  and  leave  therein 
the  substances  held  by  the  solution  or  vapor.  The  second 
case  is  where  the  same  agents  are  injected  into  a  fluid  mass, 
or,  with  such  a  mass,  into  a  fissure,  and  produce  the  given 
effect  on  a  limited  portion  of  the  same,  as  boric  and  fluoric 
acids  are  thought  to  have  produced  the  veins  of  greisen  in 
granite.  Geikie  and  other  authorities  call  these  last  segre- 
gations. 

Secretion.  This  is  a  leaching  of  portions  of  a  mass  by 
penetrating  waters  or  vapors.  The  simplest  case  is  when 
carbonated  waters  dissolve  portions  of  limestone  in  passing 
through,  and  are  forced  to  deposit  the  same,  whenever  they 
lose  their  free  acid,  as  stalagmite,  stalactite,  travertine,  etc. 
In  the  case  of  thermal  waters  they  dissolve  silica,  if  alkaline, 
and  deposit  the  same  on  cooling  or  drying,  to  form  sinter. 
Thermal  waters  or  vapors  are  thought  to  be  agents  in  the 
formation  of  some  "  veins,"  by  secreting  portions  from  the 
country  rocks,  and  depositing  them  in  fissures  or  cavities  in 
the  same.  Geodes,  amygdaloids,  etc.,  are  similarly  formed. 

Convergence.  There  are  a  number  of  more  or  less  similar 
rock  structures  that  are  due  to  the  convergence  of  similar 
molecular  compounds  ;  but  what  initiates  the  convergence, 
or  whence  and  why  the  molecules  converge,  is  unknown. 
On  assembling  the  structures  it  is  found  that  they  can  be 
grouped  according  to  whether  the  convergence  was  free  or 
restrained.  The  molecular  compounds  may  exist  in  solu- 
tion, in  a  fused  magma,  or  in  vapor. 

(a)  Free  Convergence.  This  is  shown  in  all  forms  of  crys- 
tallization where  there  was  freedom  of  growth  in  one  or 
more  directions,  as  : 


70  MANUAL    OF  LIT  HO  LOG  Y. 

1.  Crystallization  from  a  solution  or   fluid  magma,  where 
the  forms  would  be  characteristic. 

2.  Segregation,  or  crystallization  in  non-vesicular  open- 
ings in  solid  rock,  as  in  veins  and  geodes,  and  from  solutions 
or  vapors. 

3.  Vesicular  crystallization,  in  states  of  extrusive  rocks  in 
such  proximity  to  the  surface  that  the  occluded  steam  could 
expand,  but  not  escape.    This  occurs  in  rocks  of  the  highest 
acidity  (rhyolites)  as  lithophysce,  and   in  basic  rocks  under 
two  forms — with  acid  solutions,  as  calcite,  zeolites,  etc. ;  with 
alkaline  solutions,  as  crystalline  quartz  in  geodes,  or  colloid 
agate  or  chalcedony. 

4.  Sedimentary  crystallization,  when  single   crystals  or 
crystal  aggregates  form  in  fine  sediments,  from  the  intrusion 
of  saturated  solutions,  accompanied  by  some  unknown  force, 
as  pyrite  in  clay,  and  in  shales  of  the  coal  region,  and  pos- 
sibly both  are  due  to  the  same  cause.     In  the  latter  case  it 
is  the  reducing  action  of  the  organic  aggregate.     Fontaine- 
bleau  limestone  is  another  example  of  this  class;  also  den- 
dritic magnetite,  etc. 

(b)  Restrained  Convergence.  This  is  commonly  known  as 
concretion.  The  texture  of  concretions  may  be  crystalline  or 
colloid  ;  the  force  may  act  towards  or  from  the  centre,  and 
the  form  will  vary  with  the  amount  ot  restraint  opposed  by 
the  mass  in  which  the  concretion  forms  to  the  entry  of  the 
molecular  compounds.  If  the  restraint  is  equal  in  all  direc- 
tions, the  concretion  is  isometric  ;  if  unequal,  as  in  sediments 
(especially  if  of  varying  strata),  anisometric.  Under  this  we 
find  : 

1.  Crystallizations  from  a  pasty  magma,  or  simultaneous 
crystallization  of  varying  compounds,  to  produce  fibrous, 
columnar,  lath-shaped  aggregates. 

2.  The  aggregation  of  mineral  matter  in  non-crystalline 


GENERAL   DEFINITIONS.  71 

form   in  an  otherwise   crystalline  mass,  as  the  nodules  of 
mica  in  some  granites  and  gneisses. 

3.  The  same  aggregation  in  a  suddenly  cooled  mass  to 
form  spherulites,  axiolites,  etc. 

4.  The    results    of   devitrification,    as     microliths,    etc., 
perlitic  structure,  etc. 

5.  Ordinary   concretions,  which  may  be  spherical,  len- 
ticular, botryoidal,  tuberous,  pipe-formed,  etc. 

External  Structure. 

This  may  be  symmetrical  to  an  axis,  as  columnar,  stalac- 
titic,  filiform  ;  to  a  plane,  as  jointed,  stalagmitic  ;  centric, 
as  spheroidal ;  and  irregular,  as  etched,  rolled,  glaciated, 
concretionary.  The  last  two  may  have  any  or  all  of  the 
symmetrical  forms. 

Columnar.  This  is  peculiar  to  dike  and  sheet  effusions, 
and  is  due  to  cooling  (see  ante).  A  slight  columnar  struc- 
ture is  also  caused  in  pelites  by  drying  (see  ante).  In  both 
cases  the  columns  are  normal  to  the  cooling  or  drying  sur- 
face. Basalt  shows  the  structure  more  commonly  than 
other  effusives,  though  it  is  seen  in  phonolite  and  obsidian 
with  distinctness.  This  is  called  " jointing"  by  some 
authorities,  and  distinguished  from  the  ordinary  kind  by  the 
adjective  "  basaltic."  In  some  cases  only  one  series  of  frac- 
tures is  developed,  so  that  the  masses  are  tabular.  In  other 
cases  the  opposite  holds,  and  so  great  a  number  of  cracks 
are  formed  that  the  columns  are  roughly  cylindrical.  These 
are  generally  divided  by  the  fracture  parallel  to  the  walls, 
before  described,  into  rhomboidal,  cuboidal,  or  prismatic 
pieces — in  case  the  fracture  be  plane;  but,  if  irregular,  it 
causes  them  to  break  in  pieces  with  "  ball  and  socket  "  form, 
and  frequently  with  spheroidal  form. 

Stylolitic.  O.  C.  Marsh  has  shown  that  these  are  due  to 
pressure,  from  the  "  slickensided  "  appearance  of  their  sur- 


?2  MANUAL    OF  LITHOLOGY 

faces.  They  are  columnar  or  cylindrical  bodies  varying- 
from  a  fraction  of  an  inch  in  length  and  breadth  up  to  four 
inches  in  length  and  two  inches  in  diameter,  and  are  found 
at  right  angles  to  the  bedding  of  the  mass  (limestone  or 
marl),  and  are  composed  of  the  same  material. 

Cone  in  Cone.  The  same  author  suggests  a  similar  origin 
for  these  structures  which  extend  through  thin  beds  of 
limestone  or  calcareous  shale  in  the  form  of  cones.  They 
may  have  been  formed  by  pressure  on  concretions  in  process 
of  formation  (see  ante  under  "  Pressure.") 

Stalaciitic.  Solutions  formed  by  percolating  waters 
usually  find  certain  lines  of  flow  less  obstructed  than  others, 
and  the  streams  or  drops  fall  more  frequently  where  these 
lines  meet  the  surfaces  of  cavities  in  the  mass,  and  deposit 
there  portions  of  the  material  in  solution  ;  so  that  in  tin.e 
a  formation  similar  to  an  icicle  extends  from  the  roof,  and 
may  become  many  inches,  or  even  tens  of  feet,  in  length. 
Stalactites  are  common  in  limestone  caves,  under  arches  of 
masonry  (from  the  stone,  or  even  the  mortar),  under  troughs 
through  which  mineral  waters  flow,  and  may  consist  of  cal- 
cite,  fluorite,  limonite,  or  other  soluble  mineral.  They  are 
variously  colored  and  frequently  show  a  colored  banding  on 
a  transverse  fracture. 

Filiform.  This  is  seen  when  glass  tubing  is  heated  and 
pulled  apart,  or  when  artificial  mineral  wool  is  formed 
by  forcing  air  through  slag.  It  occurs  in  nature  under 
similar  conditions  when  highly  fluid  lava  is  drawn  out  by 
being  blown  into  the  air,  or  drawn  out  by  wind,  to  form 
what  the  Hawaiians  call  "  Pele's  hair."  Pele  was  the  god- 
dess of  the  nether  world. 

Jointed.  This  is  a  tendency  to  separate  into  massive 
sheets  with  parallel  bounding  planes,  and  is  generally  due 
to  warping  or  torsion  (see  ante  under  "  Pressure  ").  A 
columnar  structure  is  commonly  formed  by  the  intersection 


GENERAL   DEFINITIONS.  73 

of  two  sets  of  joint  planes ;  but  the  columns  can  be  told 
from  those  formed  from  cooling  or  drying  by  the  fact  that 
joint  columns  are  four-sided  and  frequently  square  on  a  sec- 
tion, while  the  others  are  polygonal.  While  jointing  is 
usually  on  a  large  scale  and  forms  the  external  shape  of 
masses,  it  is  frequently  so  minute  as  to  become  internal, 
and  so  frequently  repeated  as  to  resemble  cleavage.  Joint- 
ing is  not  always  apparent  in  fresh  states  of  rock,  but  shows 
only  on  weathering.  This  variety  is  called  blind  jointing  by 
miners,  and  is  used  by  them  in  "  breaking  down  "  masses. 
Jointing  is  also  called  cleat,  and  frequently,  as  in  some  coals 
and  ores,  when  there  are  two  systems  of  joints  at  right 
angles  to  one  another,  the  system  that  is  more  developed,, 
and  allows  the  mass  to  separate  more  readily,  is  called  the 
face  of  the  ore,  while  the  other  system  is  the  end.  Workings 
are  driven  against  the  cleat  or  face.  A  good  example  of 
jointing  in  metamorphic  rock  is  seen  in  the  gneiss  of  Port 
Deposit,  Md.,  where  the  mass  is  divided  into  layers  of  great 
evenness,  and  varying  from  a  few  inches  to  many  feet  in 
thickness.  Where  there  are  two  systems  of  joints  in  strati- 
fied rock,  one  is  generally  parallel  to  the  dip  (dip-joint)  and 
the  other  to  the  strike  (strike-joint). 

Spheroidal.  Under  "  Weathering "  it  was  shown  how 
angular  masses  lost  their  sharp  corners  and  acquired  a 
rounded  outline.  This  is  spheroidal  weathering.  The  same 
shape  is  seen  in  fresh  volcanic  products  when  the  explosive 
action  throws  portions  of  the  molten  mass  into  the  air  with 
a  rotary  motion,  and  they  solidify  under  this  condition,  to 
form  volcanic  bombs.  The  beginning  of  spheroidal  weather- 
ing produces  a  subangular  shape. 

Etched.  The  surface  of  soluble  rocks  is  rounded  by  the 
passage  of  solutions  over  them,  and  this  is  most  commonly 
shown  by  the  action  of  water  in  flowing  through  jointed 


74  MANUAL    OF  LITHOLOGY. 

limestone,  as  the  angular  masses  are  rounded  and  the  joints 
widened  into  fissures  and  caverns. 

Rolled.  We  can  distinguish  current-  and  wave-rolling. 
Current-rolling  takes  place  in  rivers  that  have  periodic 
currents  of  great  depth  and  velocity,  and  intercalated 
periods  of  low  water  and  weak  currents.  During  the  for- 
mer the  burden  of  trash  is  dragged  over  all  stones  too  large 
to  be  moved,  and  smaller  sizes  roll  along.  The  small  stones 
and  sand  are  whirled  over  the  bottom  so  as  to  reach  all 
sides  of  the  fixed  stones,  and  the  hollows  are  as  finely 
polished  as  the  projections,  the  sharp  contours  only  being 
rounded  off  in  hard  rocks.  The  smaller  stones  take  a  shape 
dependent  on  their  hardness  and  habit  of  fracture.  During 
the  low  waters  and  weak  currents,  which  prevail  during  the 
greater  part  of  the  year,  all  sorts  lie  on  the  river  bottom  and 
weather,  so  that  river  pebbles  vary  in  character,  being  most 
rounded  and  polished  in  torrential  streams,  and  furthest 
distributed  from  their  original  bed.  In  sluggish  streams 
with  no  rapid  currents  there  is  little  distribution  and  angu- 
lar material :  the  river  bed  representing  the  adjacent  rocks, 
while  the  average  river  pebbles  have  a  rough  and  pitted 
surface.  Wave-rolling  is  seen  on  steep  beaches,  where,  in  a 
storm,  the  grinding  of  the  shingle  under  wave  action  fur- 
nishes a  large  component  of  the  noise.  Under  this  intense 
attrition  the  friable  rocks  fall  to  sand,  and  only  the  hardest 
remain  to  be  finely  polished.  The  wrecking  of  a  Phil- 
adelphia collier  off  Nantasket  Beach,  some  years  ago,  fur- 
nished a  supply  of  anthracite  coal  in  shingle  and  sand,  but 
it  wore  away  to  powder  in  a  few  months. 

Glaciated.  The  abrasion  is  entirely  between  the  exposed 
surface  and  material  carried  by  the  ice.  Surface  glaciation 
takes  shapes  dependent  upon  the  kind  of  rock  and  the  man- 
ner of  fracturing.  In  a  hard  rock  that  exhibits  jointing  the 
surface  is  rounded  to  form  the  "  sheep-backs  "  and  "  whale- 


GENERAL   DEFINITIONS.  75 

backs "  shown  in  works  on  the  subject.  This  is  after 
the  old  surface  soil  due  to  the  long  period  of  weathering 
that  preceded  the  ice  advance  had  been  removed,  and  the 
.solid  interiors  of  the  masses  between  joint  planes  came 
under  the  planing  action  of  the  glacier,  and  resisted  it  better 
than  did  the  less  solid  portions  along  those  planes.  Softer 
shales  are  cut  down  to  a  flat  surface  if  the  material  in  the 
ice  is  of  uniform  size  ;  but  larger  and  harder  fragments  show 
their  presence  by  deep  striations.  The  ice  advance  over  a 
non-glaciated  region  has  neither  hard  rock  surface  to  act 
upon  nor  hard  material  to  drag  along,  so  that  there  may  be 
planing  at  a  distance  back  from  the  ice  front,  but  no  stri- 
ation.  The  material  carried  by  the  ice  is  rounded  only  on 
those  sides  exposed  to  abrasion  against  the  surface  ;  other 
sides  retain  their  angularity.  The  masses  carried  over  a 
hard  bottom  show  scratches  arranged  in  sets  of  parallel 
lines,  depending  on  the  variety  of  ways  they  were  held  by 
the  ice. 

Glacial  aggregation.  This  can  generally  be  distinguished 
from  sedimentation  by  the  absence  of  stratification  in  the 
mass,  and  by  the  heterogeneous  mixture  of  the  finest  clays 
with  bowlders  of  the  largest  size  without  the  slightest  trace 
-of  sorting.  Where  the  glacier  dams  a  valley  and  forms  a 
lake  a  peculiar  form  of  sedimentation  occurs — the  peculi- 
arity being  due  to  floating  ice.  In  the  still  water  the  finest 
sediments  are  distributed  to  form  a  more  or  less  sandy  clay, 
and,  from  the  continuity  of  deposition  and  uniformity  of 
deposit,  there  is  no  stratification.  This  would  not  be  very 
noticeable  were  it  not  for  the  bergs  "  calved  "  from  the  ice 
front,  which  sail  out  into  the  lake  bearing  their  burden  of 
angular  and  glaciated  material,  which  is  dropped  on  melting 
and  falls  to  the  bottom,  to  become  imbedded  in  the  clay. 
The  rounded  pieces  drop  in  straight  lines,  but  the  flat  and 
unequiaxial  pieces  fall  along  lines  of  least  resistance  from 


?  MANUAL   OF  LITHOLOGY. 

the  water  and  enter  the  mud  at  all  angles.  In  case  the  de- 
posit were  formed  by  ice  alone  on  a  glaciated  surface,  the 
pressure  would  arrange  these  with  longer  axes  parallel  to 
the  movement.  An  unstratified  clay  carrying  angular  and 
striated  or  glaciated  material  arranged  in  an  irregular 
manner  through  it  has  been  formed  in  slack  water,  and  the 
large  burden  has  been  distributed  by  ice.  In  the  event  of 
the  second  advance  of  ice  over  a  previous  glacial  deposit,, 
there  is  sometimes  a  pushing  and  distortion  of  the  old  sur- 
face, and  not  its  entire  removal. 

Concretionary.  The  structures  under  this  head  have  a 
common  convergent  origin,  but  take  a  variety  of  shapes,, 
which  depend  on  the  ease  of  access  of  the  solution  to  the 
origin  of  the  concretion,  and  growth  to  or  from  that  origin^ 
Following  J.  D.  Dana,  we  can  divide  concretions  into  cen- 
tripetal and  centrifugal ;  and  as  the  origin  is  a  point,  a  line,  or 
a  plane,  the  structure  may  be  centric,  axial,  flat,  or  irregular 
(if  it  be  wholly  anisometric).  The  texture  may  be  crystal- 
line, colloid,  or  earthy.  The  growth  may  be  continuous  or 
intermittent ;  of  considerable  size,  so  as  to  separate  masses,. 
or  so  minute  as  to  fall  under  internal  structure.  We  can- 
distinguish  concretions 

(a)  From  a  solution.     These  are  centrifugal,  and  are  due 
to  the  grouping  of  molecules  from  the  solution  about  some 
nucleus.     They  are  seen  under  process  of  formation  in  the 
waters  from  the  Carlsbad  springs.     A  section  shows  a  small 
grain  of  sand  or  speck  of  some  foreign  body  as  a  nucleusr 
which  was  rolled  about  gently  by  the  waters  and  coated 
concentrically  with  "  sprudelstein."     When  a  mass  is  built 
up  of  minute  spherules,  its  structure  is  oolitic,  and  when  the 
spherules  are  as  large  as  a  pea,  pisolitic. 

(b)  From  an  intrusion  of  a  solution  into  a  loose  mass.    The 
masses  are  usually  alluvial  clays,  marls,    chalk,   and  even 
loam.     As  these  are  sediments  and  usually  stratified,  there 


GENERAL   DEFINITIONS.  77 

will  be  a  greater  freedom  of  motion  of  the  solution  along 
bedding  planes  than  across  them,  and  the  growth  will  be 
greater  parallel  to  the  bedding  than  across  it,  so  that  flat 
concretions  will  form.  An  irregular  variation  in  porosity 
will  cause  an  irregular  shape.  Structures  under  this  class 
will  be  spherical,  lenticular,  botryoidal,  mammillary,  reni- 
form,  tuberous,  flat,  and  irregular.  In  clay  we  find  clay- 
stones,  eye-stones,  spectacle-stones,  imatra-stones,  fairy- 
stones,  where  the  solution  bears  calcite  ;  nodules  about 
pebbles,  leaves,  fish,  etc.,  in  the  clays  of  the  Carboniferous, 
where  the  solution  contained  both  calcic  and  ferrous  car- 
bonates ;  amorphous  nodules  of  pyrite  in  coal  shales,  where 
the  ferrous  sulphate  in  the  solution  was  reduced  by  the 
organic  matter  in  the  clay,  to  form  what  miners  call  "  bells," 
and  which  run  from  minute  to  large  dimensions.  In  chalk 
we  find  flint  nodules  from  the  dissolved  silica  of  sponges 
which  has  formed  around  other  sponges  or  other  siliceous 
formations.  In  loam  we  find  calcite  nodules  which,  in 
India,  are  called  "  kunkurs"  ("  nodules  "),  and  which  form 
in  openings  left  by  roots,  or  around  small  bodies,  and  furnish 
limestone  in  sufficient  abundance  for  mortar.  In  guano  and 
bone  beds  similar  concretions  of  calcic  phosphate  are  found. 
It  sometimes  happens  that  the  concretionary  mass  has 
formed  centripetally,  and  that  the  soft  interior  has  shrunk 
away  from  the  shell  and  cracked  from  drying.  The  open 
spaces  are  then  filled  with  some  mineral,  usually  calcite,  and 
form  septaria.  If  not  so  filled,  they  form  rattle-stones.  In 
highly  ochreous  clay  the  hydrated  sesquioxide  of  iron  takes 
various  forms,  and  is  called  "bean  ore  "  when  of  small  size, 
•"  ore  pots  "  when  larger  and  hollow,  "  pipe  ore  "  when  in 
axial  shapes.  Limonite  concretions  form  rapidly,  as  is 
shown  by  the  finding  of  discarded  spikes  from  the  track 
in  the  center  of  concretions  which,  have  formed  at  their 
expense. 


7%  MANUAL   OF  LITHOLOGY. 

(c)  From  a  similar  intrusion  into  a  rock  after  its  solidifi- 
cation. These  can  be  distinguished  from  the  former  by  the 
continuity  of  the  bedding  planes  through  the  concretion. 
They  are  found  in  sandstones  and  shales  from  intrusions  of 
solutions  given  above,  and  appear  to  be  formed  partly  by  the 
concretionary  power  of  the  solution,  and  partly  by  its  dry- 
ing, as  stated  under  that  topic. 

Internal  Structures. 

These  may  be  uniform  and  varied.  The  only  uniform 
structure  is  called  massive,  the  uniformity  being  local.  It  is 
possessed  by  primary  rocks,  and  shows  no  divisions  into 
strata  (layers,  beds).  Primary  rocks  are  frequently  called 
massives.  The  varied  structures  may  be  regular  and  irreg- 
ular. The  latter  are : 

Damascened  (Rutley),  as  in  some  obsidians,  where  the 
threads  of  glass  are  contorted  in  a  confused  manner  like 
the  markings  on  Damascus  sword-blades. 

Porous,  where  the  rock  is  penetrated  by  irregular  and 
often  angular  cavities,  due  to  the  removal  of  some  of  the 
minerals,  or  to  the  interstices  left  during  the  rock-formation  ; 
not  due  to  gas.  If  the  openings  are  large,  it  is  cavernous. 

Regularly  Varied  Structures.  These  may  be  (a)  bounded 
by  spherical  surfaces,  or  (b)  repetitions  symmetrical  to  a 
plane,  warped  surface,  straight  or  wavy  line.  The  former 
will  be  called  spherical,  the  latter  parallel,  structures. 

(a)  Spherical  Structures. 

Cellular.  This  term  is  applied  to  rocks  containing 
cavities  more  or  less  rounded  from  the  expansion  of  gas 
during  effusion.  They  are  generally  quite  spherical  if 
the  motion  of  the  mass  had  stopped  before  it  became  so 
pasty  as  to  resist  the  expanding  force  ;  if  the  contrary 
state  existed,  the  structure  will  be  described  later.  The 


GENERAL   DEFINITIONS.  79 

structure  is  most  commonly  met  with  in  surface  portions 
of  compact  effusives.  If  the  cells  are  few  and  isolated, 
the  state  is  called  vesicular;  if  they  occupy  an  equal  space 
with  the  solid  part,  it  is  styled  scoriaceous,  or  slaglike  ;  if  the 
cavities  predominate,  pumiceous,  or  foamlike.  When  the 
cavities  become  filled  with  agate,  calcice,or  zeolites  leached 
from  the  walls,  the  state  is  amygdaloidal.  In  obsidians  sim- 
ilar cavities,  called  lithophysce(\.  Richthofen),  are  thought  by 
J.  D.  Dana  to  have  been  filled  with  an  aqueo-igneous  or 
jelly  like  secretion,  which,  by  alternate  crystallization  and 
drying,  forms  a  series  of  concentric  crystalline  spheroids  of 
solid  or  spongy  character.  The  minute  crystals  are  of 
quartz,  tridymite,  feldspar,  topaz,  and  garnet. 

Geodic,  when  cavities  of  any  shape  are  lined  with  crys- 
tals, but  not  completely  filled.  In  some  cases  layers  of 
chalcedony  occur  under  the  crystalline  layer.  If  the  crys- 
tals are  minute,  the  structure  is  drusy. 

Spherulitic,  GlobuliferouSj  and  SpJierophyric  (J.  D.  Dana). 
This  is  a  concretionary  structure  found  in  eruptives,  and  is 
formed  during  the  plasticity  of  the  mass,  as  shown  by  the 
elongation  of  spherules  by  its  motion.  It  occurs  megascopic 
from  concretions  of  mica,  or  feldspar  and  mica ;  or  micro- 
scopic from  the  formation  of  spherulites  which  are  radially 
crystalline.  A  not  very  common  form  of  spherules  is  caused 
by  the  fusion  of  pyroclastic  fragments  of  the  country  rock 
in  the  intrusive  fluid.  A  good  example  is  seen  in  the  spheres 
of  willemite  in  the  dikes  cutting  the  ore  body  in  the  New 
Jersey  zinc  mines. 

Perlitic.  This  is  characteristic  of  perlite,  but  is  found  in 
other  vitreous  rocks.  During  cooling  the  mass  is  fissured 
by  minute  cracks  that  form  spheroids  and  ellipsoids,  whose 
section  shows  concentric  coats.  This  is  held  by  some 
authors  to  be  similar  to  the  spheroidal  jointing  shown  on  a 
greater  scale  by  basalt,  etc. 


SO  MANUAL    OF  LITHOLOGY. 

(V)  Parallel  Structures. 

Those  symmetrical  to  planes  and  warped  surfaces  will 
be  called  flat  parallel;  those  symmetrical  to  lines,  linear 
parallel. 

The  flat-parallel  structures  are  : 

Bedded,  Stratified.  Stratification  has  been  already  de- 
scribed. We  distinguish  seams,  or  thin  layers  differing  in 
character  from  those  above  or  below  ;  beds,  as  thick  seams ; 
bedded  masses,  when  the  horizontal  dimensions  are  inconsid- 
erable in  comparison  with  the  thickness  ;  lenticular  masses, 
when  beds  thin  out  and  appear  to  be  isolated  in  a  stratified 
deposit.  The  varieties  of  bedding  are  : 

Massive,  when  of  great  thickness,  and  not  divisible  into 
layers. 

Straticulate  (J.  D.  Dana),  when  made  up  of  even  and  thin 
layers,  separate  or  not,  as  in  clay,  stalagmite,  agate,  etc.  It 
is  also  called  banded. 

False  bedding  {K.  Geikie)  includes  all  kinds  that  are  formed 
otherwise  than  by  distribution  in  still  water,  as  : 

(a)  Current-bedding,  where  the  stream  pushes  the  detritus 
along  irregularly,  so  that  the  front  has  a  slope  of  2O°-35°, 
and  the  successive  deposits  are  parallel  to  this  slope.     In  an 
estuary  the  alternating  slack  waters  deposit  horizontal  layers, 
so  that  regular  and  cross-bedded  layers  are  intercalated. 

(b)  Flow-and-plunge   structure    exhibits   a   curved    cross- 
bedding  that  is  without  intercalated  regular  bedding.     It 
occurs  where  waves  work  over  a  supply  of  sand  and  fine 
gravel,  and  is  seen  on  shores  and  sometimes  in  sub-glacial 
deposits. 

(c)  Beach  structure  is  a  similar  case,  but  exhibits  a  varia- 
tion in  angle  of  bedding  at  the  level  of  high  tide.     Above 
that  the  beach  has  a  slight  slope ;  below,  a  steeper  one. 

(d)  Wind-drift    structure  is    composed    of    Straticulate 


GENERAL   DEFINITIONS.  8 1 

layers  in  positions  oblique  to  one  another.  It  is  caused  by 
variations  in  wind  direction  in  a  sandy  region. 

Trough-bedding  (Ger.  Muldenformig),  when  sediment  is 
deposited  in  a  depression,  and  takes  the  shape  of  the  same  ; 
but,  owing  to  the  slipping  of  the  sediment  down  the  slopes, 
the  layers  are  thicker  in  the  trough  than  on  the  sides,  and, 
eventually,  the  depression  is  filled,  and  the  overlying  layers 
become  horizontal.  A  good  example  is  seen  in  the  Mesozoic 
coal  basins  in  Virginia,  where  the  deposit  is  in  hollows  in 
the  Archaean  rocks. 

Cloaklike  Bedding  (Ger.  Mantelformig),  where  a  sinking 
of  the  surface  causes  a  lake  or  ocean,  and  the  hills  and 
smaller  elevations  are  gradually  submerged  or  "  cloaked  " 
by  the  by  the  sediment.  This  is  seen  on  a  large  scale  in 
the  bottom  of  Lake  Bonneville,  Lake  Lehontan,  etc.  Here 
the  strata  dip  in  all  directions  from  the  submerged  mass. 
This  and  trough-bedding  must  not  be  confounded  with 
synclinals  and  anteclinals,  which  are  caused  by  flexing  beds 
originally  horizontal  and  parallel,  while  the  above  were 
never  horizontal,  and  always  thicker  at  their  lower  than 
their  upper  parts. 

Veined.  A  vein  is  a  parallel  and  "  comblike  "  arrange- 
ment of  crystalline  matter  in  an  open  fracture  in  older  rocks. 
The  crystals  usually  have  their  longer  axes  —  especially  in 
the  vein  matter  —  normal  to  the  walls  of  the  fracture. 
Alternations  in  the  solutions  cause  variations  in  the  minerals, 
and  the  layers  are  deposited  on  one  another  till  they  meet 
in  the  centre  of  the  fracture.  The  parallel  arrangement  of 
vein  matter  is  not  like  the  similar  arrangement  of  stratified 
matter,  as  in  the  first  there  is  a  repetition  of  the  order  of 
succession  of  the  deposits  on  either  side  of  the  middle  of 
the  vein,  while  there  is  generally  no  symmetry  in  the 
stratification  of  a  bed.  The  vein,  also,  is  crystalline ;  the 
bed,  clastic.  The  varieties  of  veins  and  their  origin  belong 
to  economic  geology.  One  of  the  most  common  vein- 


82  MANUAL   OF  LITHOLOG  Y. 

formers  is  quartz,  and  it  fills  the  small  cracks  in  sandstones 
with  material  more  dense  than  the  rock,  so  that  weathering 
brings  them  into  relief. 

Fissured,  Fractured,  where  rocks  have  been  deformed 
and  crushed.  In  case  the  walls  of  the  fissure  have  been 
moved  on  one  another,  the  grinding  forms  slickensides. 
These  may  be  grooved  or  plane.  The  soft  shales  of  the 
coal  frequently  have  been  grooved;  but  their  softness  would 
have  allowed  the  evidence  to  be  lost  were  it  not  for  the 
filling  of  the  fissure  with  quartz,  which  has  preserved  a  cast 
of  the  same  with  the  minute  groovings.  In  case  the  rocks 
are  pyritiferous,  the  movement  produces  a  plane  surface 
with  a  mirror-like  polish  ;  but  weathering  blackens  the  same 
without  entirely  destroying  the  lustre.  In  erogenic  move- 
ments the  rocks  are  sometimes  finely  crushed,  and  Bonney 
claims  this  as  preliminary  to  one  form  of  schistocity. 

Fissile.  This  is  a  general  term  for  a  tendency  in  rocks  to 
split  more  or  less  readily.  We  can  distinguish 

(a)  Shaly   (Laminated},  where   there  is  an   arrangement 
in  layers,  relatively  parallel,  and  a  tendency  to  split  along 
the  layers.     This  is  also  called  stratified,  and  fine  layers  are 
straticulate  or  laminated.     The  texture  is  generally  fine,  as 
in  pelites. 

(b)  Schistose  (Foliated),  with  the  layers  wavy  through  the 
somewhat  parallel  arrangement  of  unequiaxial  minerals,  or 
those  that  are  eminently  cleavable  in  one  direction,  as  mica, 
talc,  chlorite,  hornblende,  etc.     The  thin   flakes  are  called 
folia.     The    texture    of    schists  is  crystalline,  and    coarser 
than  the  clastic,  or  crystalline-clastic  texture  of  shales. 

(c)  Slaty   (Cleaved),  with    a    tendenc}^    to    split   in    thin, 
sheets  parallel  to  a  given  plane,  and  with  a  fine  and  homo- 
geneous  texture.     It   is  produced   by  pressure,  as  before 
stated  (p.  63),  and  is  known,  in  coarse-grained  rocks,  as  a 
species  of  jointing. 

We  distinguish  the  varieties  of  cleavage  as  follows :  (i) 


GENERAL  DEFINITIONS.  83 

If  parallel  to  the  bedding,  and  in  fine  texture,  it  is  generally 
shaly  lamination  ;  if  in  a  coarse  texture,  flagstone-  QV  flagband- 
cleavage.  (2)  If  at  an  angle  to  the  bedding,  and  in  a  fine 
texture,  slaty-cleavage. 

Streaked,  Fluxion  Structure  (A.  Geikie),  Banded  (Rutley), 
Fluidal  (J.  D.  Dana).  The  term  "  streaked  "  is  indefinite ; 
"  banded  "  is  applied  to  other  structures,  as  in  agate,  onyx, 
etc. ;  and  neither  affords  information  regarding  the  origin  of 
the  structure,  which  is  peculiar  to  igneous  rocks.  Geikie 
defines  it  as  "  having  some  or  all  of  the  component  minerals 
arranged  in  streaky  lines,  either  parallel  or  convergent,  and 
often  undulating."  (This  last  would  include  Rutley 's 
"  damascened ").  He  further  states  that  it  is  found  less 
marked  in  crystalline  rocks,  as  diorite  and  dolerite.  Dana 
defines  it  as  "  having  the  material  of  the  rock  or  of  portions 
of  it  in  parallel  lines  or  bands  and  looking  as  if  due  to  the 
flow  of  the  rock  while  melted."  He  further  speaks  of  the 
"  thin  laminated  structure  "  of  trachytic  and  andesitic  lavas 
as  due  to  successive  action  in  the  supply  of  lava  to  the  point 
of  outflow,  and  refers  to  Iddings.  There  are  a  number  of 
structures  thus  referred  to  "  flow":  (i)  a  banding  of  the  rock 
in  laminae,  as  in  the  lavas  above  mentioned,  and  in  "  slaty  " 
porphyry  —  this  structure  causes  the  rock  to  break  a  little 
more  readily  along  than  across  the  laminae  ;  (2)  a  stretching 
of  the  rock  by  the  flow  so  as  to  show  a  structure  like  that 
in  pulled  molasses  candy  ;  (3)  a  stretching  of  vesicles  in  the 
line  of  flow,  so  that  they  are  no  longer  spherical,  but  pear- 
shaped  or  elongated  ;  (4)  a  fissuring  or  fracturing  of  pheno- 
crysts  by  movements  of  a  pasty  matrix.  The  experiments 
of  Tresca  on  "  flow  "  in  solids  have  been  improved  upon  by 
Townsend,  whose  exhibits  show  on  polished  and  etched 
sections  the  particles  arranged  along  "  fluxion  "  lines,  as  in 
the  states  of  rocks  just  noted.  While,  therefore,  it  may  be 
possible  for  this  structure  to  be  formed  in  solidified  rocks, 


84  MANUAL    OF  LITHOLOGY. 

it  is  generally  exhibited  in  movements  during  a  pasty  state, 
though  the  fissured  phenocrysts  show  that  motion  followed 
initial  crystallization. 

Linear-parallel  structures : 

The  second  and  third  varieties  of  the  last  structure  are 
linear  parallel,  but  cannot  be  well  separated  from  the  others. 
Also: 

Fibrous,  where  some  of  the  mineral  components  are  com- 
posed of  distinct  fibres,  as  in  gypsum,  satin-spar,  chrysotile, 
amianthus,  asbestus,  etc.  Some  concretions  are  fibrous,  but 
they  do  not  fall  here,  as  they  are  convergent. 

Lathy,  where  some  or  all  of  the  components  are  in  flat 
or  twisted  lath-shaped  forms,  as  in  some  diabases,  cyanite 
rock,  etc. 

Implication  Structure,  where  there  has  been  a  peculiar  and 
regular  infolding  of  one  another  by  two  synchronously 
formed  ingredients  of  a  rock  (Zirkel),  as  by  the  quartz  and 
feldspar  in  pegmatite,  where  the  quartz  is  systematically 
arranged  on  certain  of  the  cleavage  planes  of  the  feldspar 
so  as  to  produce  characters  that  have  been  likened  to 
Hebrew,  Assyrian,  etc.,  and  the  rock  called  graphic  granite -, 
The  structure  is  also  called  pegmatitic. 

A  number  of  (m)  structures  are  omitted  here. 

Fulgurite.  The  effect  of  lightning  on  the  earth's  surface 
is  to  fuse  the  rocks  to  varying  depths  and  produce  a 
natural  glass  therefrom,  which  is  called  fulgurite.  In  solid 
rocks  this  may  be  only  a  surface  fusing,  but  in  sands  there 
is  sometimes  a  tube  of  considerable  length  (up  to  ten  feet) 
thus  formed.  Fulgurites  are  indicated  by  glassy  patches, 
drops,  or  tubes  on  rocks,  and  are  found  most  frequently 
on  the  tops  of  high  peaks.  In  sand  the  tubes  may  be  three 
inches  across.  This  form  of  glass  is  distinguished  by  the 
absence  of  microlites,  thus  showing  its  sudden  cooling. 


GENERAL  DEFINITIONS.  8$ 

COMPOSITION. 

This  refers  to  the  average  constitution  of  the  rock,  and 
the  terms  used  are  derived  from  chemical,  mineral,  or 
structural  peculiarities,  as : 

Calcareous,  containing  carbonate  of  lime. 

Felsitic  (Felsophyric,  J.  D.  Dana),  having  feldspar  as  a 
principal  ingredient. 

Arenaceous,  composed  of  sandlike  grains. 

Argillaceous,  consisting  of  clayey  matter. 

Ferruginous,  cemented  by  or  containing  oxide  or  car- 
bonate of  iron.  The  last  is  sometimes  called,  in  waters, 
chalybeated. 

Siliceous,  Quartzose,  containing  silica — the  former  in  a 
colloid,  the  latter  in  a  crystalline,  form.  The  converse  of 
the  latter  is  quartzless,  and  refers  only  to  the  absence  of  the 
crystalline  mineral,  and  not  to  the  absence  or  poverty  of 
the  chemical  compound,  as  in  basic. 

Acid,  containing  siliceous  acid  in  chemical  composition 
to  such  an  extent  that  it  forms  the  larger  portion  of  the 
rock  constitution.  The  converse  is  basic.  (See  p.  4.) 

HARDNESS. 

This  refers  to  the  original  state  of  the  rock,  and  not  to 
the  hardness  after  weathering.  This  change  increases  the 
hardness  of  some  sandstones,  limestones,  and  all  sinters  ;  but 
reduces  that  of  felsophyres.  The  scale  of  Mohs  is  uni- 
versally used. 

FRACTURE. 

This  depends  on  texture  and  structure,  with  slight 
variations  between  fresh  and  weathered  states,  such  as: 

Conchoidal,  when  the  broken  surface  exhibits  shell-like 
forms,  convex  or  concave,  as  in  the  glassy  states  of  rocks 
and  artificial  products. 


86  MANUAL   OF  LITHOLOGY. 

Splintery,  when  the  surface  is  covered  with  partially 
separated  splinters  in  irregular  fibers. 

Smooth,  when,  without  being  plane,  the  surface  presents 
no  irregularities. 

Tabular,  when  the  mineral  forms  the  greater  portion  of 
the  rock,  and  possesses  a  highly  developed  cleavage,  as  in 
some  hyperites. 

Crumbly,  when  the  surface  is  slightly  loose  and  sandy, 
as  in  protogine-granite. 

Foliated,  Laminated,  Slaty,  can  be  inferred  from  previous 
definitions. 

Irregular,  when  the  surface  exhibits  none  of  the  above 
regular  fractures. 

COLOR. 

The  color  given  in  each  case  is  that  of  the  fresh  fracture 
of  a  rock,  as  many  rocks  change  the  color  on  weathering  or 
even  exposure  to  the  air  for  a  few  seconds,  in  the  same  way 
as  the  colors  on  buried  wall-paintings  or  statues  that  are 
uncovered  after  lying  for  centuries  fade  quickly  on  exposure 
to  air  and  light.  When  certain  colors  are  characteristic  of 
fresh,  and  others  of  weathered,  states  of  the  same  rock,  the 
variation  is  one  means  of  identification,  as  in  phonolite.  In 
general,  it  can  be  stated  that 

White  shows  an  absence  of  iron  or  other  heavy  metallic 
oxides,  either  in  the  original  composition  of  the  rock  or 
owing  to  subsequent  change ;  but,  if  they  occur,  they  have 
usually  been  reduced  to  the  pyritiferous  form  by  organic 
•components  of  the  rock,  and  are  returned  to  the  oxide  form 
by  weathering.  Rocks  containing  no  oxides  are  marble, 
.gypsum,  white  kaolin,  fire-clay,  etc.;  under  rocks  weathered 
white  are  some  basic  eruptives,  especially  when  under  peat 
swamps. 

Black  indicates  carbon,  magnetite,  or  a  heavy  bisilicate 


GENERAL   DEFINITIONS.  87 

{hornblende,  pyroxene,  etc.).  In  the  Wyoming  (northern) 
anthracite  basin  the  surface  is  highly  cultivated,  and  the 
spring  and  fall  ploughings  show  the  outcrops  of  the  various 
beds  marked  by  bands  of  blacker  soil.  The  writer  has  seen 
strings  of  magnetite  rotted  soft  in  a  drift-face  driven  to 
strike  a  hoped-for  ore  body. 

Yellow,  Dull  yellow  in  a  volcanic  region  may  be  due 
to  sulphur,  but,  in  general,  it  indicates  iron  ocher;  bright 
yellow  is  due  to  pyrites.  The  ochers  come  from  the  oxida- 
tion of  ferruginous  compounds  to  form  limonite.  They  are 
seen  lining  the  ditches  through  which  waters  from  coal 
mines  flow,  or  from  springs  in  pyritiferous  rocks,  and 
therefore  indicate  pyrite  or  marcasite  at  depths. 

Brown  indicates  lignite,  or  hydrated  iron  or  manganese, 
and  the  umbers  are  allied  to  the  ochers  in  origin. 

Red  is  due  to  anhydrous  ferric  oxide.  It  is  a  transition 
state  in  the  process  of  complete  oxidation,  and  is  common  to 
weathered  pyritiferous  lodes.  In  fresh  rock  it  is  seen  to 
advantage  in  jasper;  in  weathered  rock  it  forms  the  "iron 
hat "  of  the  miners,  and  gives  rise  to  the  well-known  proverb 
in  all  tongues,  that  may  be  freely  translated : 

"  No  gangue  so  good  as  that 
Which  wears  an  '  iron  hat.' " 

J.  D.  Dana  says  that  the  red  color  of  many  sandstones  is 
-due  to  a  small  amount  of  heat  that  the  rocks  have  received 
during  consolidation,  as  shown  by  the  reddening  of  light- 
colored  sandstones  bp.,  and  that  the  color  of  the  Triassic 
rocks  on  the  Atlantic  border  of  the  United  States  is  due  to 
the  heating  of  the  rocks  and  waters  by  trap  effusions,  so  that 
high  oxides  of  iron  were  distributed. 

Green  is  found  in  rocks  poor  in  silica  and  free  quartz.  If 
schistose,  the  color  is  due  to  talc,  chlorite,  serpentine,  etc.; 
if  massive  and  crystalline,  to  chlorites.  Some  intrusive 


88  MANUAL   OF  LITHOLOGY. 

rocks  were  named  "  greenstones  "  from  this  characteristic. 
Decomposed  copper  ores  sometimes  make  green  crusts  or 
stains  ;  but  these  are  on  the  surface  only,  and  are  not  seen 
on  fresh  fractures,  except  in  malachite. 

Lustre,  feel,  smell,  specific  gravity,  and  other  properties  of 
rocks  and  minerals  are  used  as  in  mineralogy. 

Replacement  is  a  term  used  to  denote  the  seemingly 
gradual  withdrawal  of  one  mineral  from  the  rock  and  the 
taking  of  its  place  by  another.  A  dolerite  is  composed  of 
pyroxene  and  labradorite.  We  find  associated  with  dolerites 
a  rock  with  little  or  no  labradorite,  but  a  great  deal  of  nephe- 
line,  and  we  call  it  nepheline-dolerite,  and  say  that  the 
nepheline  has  replaced  the  labradorite.  The  replacement  has 
taken  place  at  the  formation  of  the  rock,  by  some  influence 
that  caused  nepheline  to  crystallize,  rather  than  labradorite. 
A  comparison  of  the  analyses  of  feldspar-basalt  and  nephe- 
line-basalt  shows  a  difference  of  .009  in  silica,  .01  in  lime, 
and  .0004  in  soda,  while  the  other  ingredients  vary,  in  the 
two  rocks  analyzed,  as  greatly  as  in  two  specimens  of  the 
same  rock  from  different  localities.  The  "  replacement  " 
of  mica  by  hornblende  or  augite  makes  the  varieties  of 
hornblende  and  augite-granite.  "  Replacement "  is  used  in 
the  definitions  of  varieties  of  the  same  rock. 

SUDDEN  AND  LOCAL  CHANGES  IN  ROCKS. 

In  the  faces  of  some  granite  quarries  there  are  "  segre- 
gations "  of  the  same  rock  with  the  crystals  of  enormous 
size,  called  "giant  granite,"  or  streaks  of  "  greisen,"  which 
are  limited  in  extent.  These  are  due  to  changes  in  the 
rapidity  of  cooling,  or  to  impregnations  during  the  fused 
state.  In  the  same  fissure  two  massive  rocks  run  parallel 
to  one  another  for  a  short  distance;  but  within  slight 
distances  each  may  be  the  envelope  of  the  other.  As  both 
are  fresh,  the  change  must  have  originated  by  differentia- 


GENERAL  DEFINITIONS.  89 

tion  in  a  common  magma  during  eruption.  The  changes 
from  "  contact  metamorphism  "  have  been  already  noted, 
and  can  be  recognized  by  the  study  of  the  region.  In 
the  case  of  sedimentary  rocks  the  variations  are  frequent 
and  of  limited  extent.  They  may  be  due  to  a  number  of 
causes : 

To  a  system  of  currents  of  greater  intensity  over  parts  of 
the  area  of  deposit.  J.  F.  Blandy  was  the  first  to  map  the 
river  systems  during  the  Carbonic  era  by  the  erosions  of  the 
beds  during  deposit  and  the  filling  of  the  basins  with  the 
material  of  the  top  rock.  Such  a  case  is  seen  when  the  bed 
thins  rapidly  by  the  coming  down  of  the  top  rock  for  a  short 
distance,  and  its  sudden  rising  again. 

To  a  sudden  change  in  the  conditions  of  deposition,  as  pelites 
are  indications  of  deep  water  or  feeble  currents,  or  both ; 
while  gravels  are  indications  of  currents  of  considerable 
force.  The  writer  has  seen  in  the  middle  of  a  coal  seam 
(twelvefeet  thick)  a  "  parting"  of  fine-grained  shale,  averaging 
seven  inches  in  thickness,  that  held  a  lenticular  seam  of  coarse 
conglomerate  two  inches  thick,  and  a  few  feet  in  length  and 
width.  The  examination  of  the  same  parting  throughout 
the  mine,  and  throughout  the  region,  failed  to  show  a  paral- 
lel instance.  E.  Orton  reports  in  the  coal  of  northeastern 
Ohio,  two  feet  below  the  top  of  the  bed,  an  angular  frag- 
ment of  quartz  vein-stuff,  as  fresh  as  if  just  broken  from  the 
parent  mass.  The  coal  adhered  to  it  on  all  sides,  and  had 
evidently  accumulated  about  it,  as  it  was  undisturbed. 

To  a  variation  in  conditions  subsequent  to  rock-formation. 
Quarry  faces,  as  in  the  Siluro-Cambrian  of  Pennsylvania, 
sometimes  show  that  variations  in  porosity,  or  other  causes, 
have  allowed  magnesia  solutions  to  penetrate  to  different 
depths  in  limestone  beds,  so  that  thecalcite  has  been  irregu- 
larly turned  to  dolomite,  and  the  same  hand  specimen  will 


90  MANUAL    OF  LITHOLOGY. 

consist  of  both,  with  the  line  of  separation  running  across 
bedding  lines. 

The  age  of  rocks  can  be  relatively  determined  as  follows  : 
A   rock  is  always  older  than  tJiat  which  is  deposited  on  it. 
In  case  no  subsequent  movement  has  taken  place  it  will  show 
that  the  upper  rock  is  the  younger  of  the  two.     The  excep- 
tions are : 

(a)  When  a  fracture  has  occurred  along  a  bedding  plane, 
and  a  fluid  sheet  has  been  intruded   into  the  fracture,  or 
when  the  fracture  has  been  filled  by  vein  material.     While 
the  sheet  or  vein  is  younger  than  the  overlying   rock,  its 
recency  can  be  shown  by  its  containing  fragments  of  the 
same — as  "  breccia  "  in  the  first  case,  and  as  "  horses  "  in  the 
second. 

(b)  When  the  whole  formation  has  been  overturned.     In 
this  case  the  oldest  beds  are  brought  on  top,  and  the  study 
of  a  limited  area  might  mislead  the  observer,  were  it  not 
that,  in  certain  cases,  the  top  and  bottom  rocks  of  a  bed  are 
plainly    marked,  as  in  coal,  by  the  former  containing  the 
trunks  and  foliage  of  the  vegetation,  and  the  latter  the  roots. 
Top  sandstones  near  a  bed  carry  the  trunks  and  branches  of 
vegetation  ;  bottom  sandstones  in   similar  conditions  carry 
nothing,  but  frequently  become  more  argillaceous.     In  the 
case  of  a  conglomerate  we  can  usually  tell  an  overturn  by 
finding  the  argillaceous  partings  that  frequently  occur  in  it 
or  bounding  it,   and    noting   on    which  side   the    greatest 
amount  of   ferruginous   staining   occurs  :    that  will  be  the 
side  that  was  uppermost  during  deposition,  as  in  gravel  the 
percolating  waters   leach  the  iron  from  the  mass  and  carry 
it  downwards  till  stopped  by  the  impervious  strata,  and  de- 
posit it  therein  or  in  the  last  few  inches  or  feet  of  the  porous 
portion  —  depending   on  the  amount — of  the  gravel  bed. 
After  solidification  that  remains  as  a  witness  of  the  position 
during  deposition. 


GENERAL   DEFINITIONS.  9 1 

A  rock  is  always  older  than  one  that  has  disturbed  it.  The 
case  of  an  intruding  sheet  or  vein  has  been  just  described. 
In  the  case  of  veins  or  apophyses  intersecting  one  another, 
the  younger  cuts  the  older.  If  two  igneous  sheets,  or  two 
veins,  lie  parallel  to  one  another  in  the  same  fissure,  and  have 
been  formed  at  different  times,  the  younger  will  contain 
fragments  of  the  older,  as  above  stated.  The  exceptions 
are  : 

(a)  When  a  cloak  bedding  (p.  81)  has  been  so  removed 
by  erosion  that  the  underlying  rock  is  exposed,  it  seems  to 
have  been  projected   from  below  and   to  have  raised   the 
•overlying  strata. 

(b)  When  a  soluble  bed  has  been  dissolved  and  the  over- 
lying strata  have  been  fractured  in  the  resulting  settling, 
as  in  the  case  of  caverns  in  salt  or  limestone. 

The  relative  level  of  two  rock-formations  is  no  criterion 
of  their  age,  as  the  oldest  rocks  may  be  shoved  upward  by 
orogenic  movements,  or  left  by  erosion.  In  eastern  Penn- 
sylvania the  Potsdam  sandstone  and  overlying  limestone 
have  been  carried  in  patches  upward  with  the  Archaean  mass 
to  form  the  South  Mountain,  and  thus  rise  hundreds  of  feet 
above  the  much  younger  Mesozoic  rocks  to  the  south  and 
the  slates  to  the  north.  The  Oriskany  and  Medina  forma- 
tions make  parallel  ridges  in  the  same  region  that  remain 
intact,  while  the  Marcellus  (older  than  the  former)  and 
Lower  Helderberg  (older  than  the  latter)  form  deep  valleys 
on  their  northern  flanks. 


THE  ROCKS. 


We  are  acquainted  with  the  components  of  the  crust  at 
limited  depths  by  the  deformation  of  some  portions  and 
their  exposure  through  denudation.  It  has  been  observed 
that  each  portion  of  the  crust  maintains  a  temperature  de- 
pendent on  the  local  annual  mean  at  its  surface,  but  that 
there  is  an  increase  on  going  towards  the  centre.  With  a 
constant  pressure  at  all  depths  there  would  finally  be 
reached,  even  at  the  lowest  rate  of  increase,  a  depth  whose 
temperature  would  suffice  to  fuse  all  known  substances, 
without  the  aid  of  moisture,  which  lowers  the  temperature 
of  fusion.  Volcanic  extrusions  prove  that  such  tempera- 
tures exist  at  depths,  and  with  an  abundance  of  moisture,  as 
the  accompanying  gases,  which  cause  the  explosive  effects 
of  eruption,  contain  99$  of  water.  Astronomically  the  earth 
acts  as  a  rigid  body,  so  that  geologists  agree  that  it  is  prac- 
tically solid,  and  that  whatever  portion  exists  of  sufficient 
temperature  to  be  fluid  at  ordinary  pressures  must  consist 
of  an  interstratum,  between  the  centre  and  crust,  so  strongly 
compressed  as  to  act  as  a  solid,  but  which  may  become  lo- 
cally fluid  by  crustal  adjustments  which  abate  the  pressure. 
The  portion  thus  liquefied  may  have  been  formerly  at  or 
near  the  surface  as  a  solid  rock,  or  an  aggregate  of  sedi- 
ments with  its  interstitial  water.  In  either  case  an  absolute 
fluidity  would  destroy  all  traces  of  original  structure  and 
allow  a  rearrangement  of  molecules.  A  cooling  of  this 

92 


THE  ROCKS.  93 

magma  would  produce  a  rock  which,  as  far  as  structure  or 
texture  is  concerned,  might  have  been  formed  in  the  earliest 
geological  period  ;  but,  as  far  as  origin  is  considered,  may  be 
a  complete  metamorphism  of  an  aggregate  of  later  sedi- 
ments. All  rocks  formed  from  a  state  of  fluidity  such  that 
absolute  freedom  of  motion  existed  among  the  molecules 
will  be  called  primary  eruptive,  or  massive  ;  the  terms  massives 
and  eruptives  will  also  be  applied. 

In  a  fluid  magma  of  one  element  there  would  be  no 
tendency  to  disassociation,  and  no  crystallization  till  the  tem- 
perature approached  the  point  of  saturation.  In  nature  the 
magma  contains  a  large  number  of  elements  of  varying  af- 
finities and  gravities,  and  capable  of  forming  bodies  of  widely 
varying  fusibility.  Sorby  was  the  first  to  propose  a  theory 
of  segregation  of  magmas  into  strata  of  varying  densities  or 
fusibilities,  and  this  was  modified  by  v.  Richthofen  to  account 
for  an  order  of  effusions  in  a  given  district.  Iddings  has 
lately  formulated  a  law  that  the  effusions  from  a  magma  are 
primarily  of  its  average  composition,  but  are  subsequently 
differentiated  so  that  later  outpourings  become  nearer  the 
extremes  of  acidity  and  basicity  with  the  lapse  of  time,  and 
the  final  ones  reach  those  extremes.  In  studying  the  extru- 
sions of  a  region  that  are  of  nearly  the  same  age,  and  in  the 
examination  of  a  specimen  under  the  microscope,  it  is  found 
that  differentiation  takes  place  before  and  after  extrusion,  so 
that  from  a  magma  of  mean  composition  there  may  be  dif- 
ferentiated two  outflows,  which  show  their  origin  by  their 
intimate  association,  as  an  acid  aplite  and  a  basic  minette 
from  a  granitic  magma,  a  camptonite  and  bostonite  from 
gabbro.  The  two  outflows  are  found  frequently  in  the 
same  fissure,  and,  locally,  each  as  the  envelope  of  the  other. 
It  has  been  abundantly  proven  that  the  most  basic  rocks 
are  of  the  lowest  fusibility,  and  first  to  crystallize  ;  that  the 
mineral  components  of  a  given  rock  form  in  the  order  of 


94  MANUAL    OF  LITHOLOGY. 

their  acidity  ;  and  that  the  bath  becomes  more  acid  after 
each  crystallization,  so  that  quartz, — the  most  acid, — if  pres- 
ent, fills  the  residual  interstices.  It  has  also  been  frequently 
shown  that  the  crystals  sink  in  the  bath.  Zirkel  notes 
instances  in  granite  apophyses  where  the  intruding  rock  lost 
first  its  basic  content  of  phenocrysts  (mica),  next  the  feldspar,, 
so  that  the  ends  contained  granular  quartz  only  ;  and  in  ex- 
trusions  of  obsidian  Becker  notes  that  the  upper  portions  are 
frequently  free  from  crystals,  and  are  most  acid,  while  the 
crystals  are  accumulated  at  the  bottom  of  the  flow.  Zirkel 
has  compiled  a  multitude  of  rock  analyses  to  show  that 
the  groundmass  of  a  rock  is  more  acid  than  the  rock 
average. 

Rosenbusch  calls  the  period  of  original  crystallization  in. 
the  hot  abysses  intratelluric.  With  a  slow  rate  of  cooling 
the  intratelluric  crystals  would  continue  to  grow  as  long  as- 
the  bath  maintained  its  fluidity,  and  was  sufficiently 
saturated  with  the  necessary  molecules;  or  until  the  arrival 
of  a  period  when  other  compounds  began  to  crystallize  ;  or,, 
again,  until  the  temperature  of  the  bath  fell  below  the  point 
of  fluidity.  As  the  bath  became  crowded  with  crystals  the 
interstitial  spaces  would  become  constricted,  and  those 
minerals  subsequently  formed  would  be  obliged  to  modify 
their  shape  unless  they  could  push  aside  the  enclosing 
members  of  former  crops,  until  the  mass  became  solid  from 
the  closing  of  these  irregular  and  gradually  diminishing  in- 
terstices by  those  last  to  crystallize.  The  first  to  form  do 
not  always  attract  all  of  the  molecular  compound  in  the  bath, 
as  the  second  generations  frequently  show  repetitions  of  the 
intratelluric  forms  in  the  groundmass.  If  an  eruption  should 
take  place  during  the  formation  of  the  intratelluric  crystals,, 
they  would  be  dashed  against  the  walls  of  the  fracture,, 
through  which  the  mass  would  be  forced,  and  eroded,  frac- 
tured, or  fissured  by  the  impact ;  or  would  be  drawn  out,. 


THE   ROCKS.  95 

twisted,  or  otherwise  deformed  if  the  bath  were  pasty.  All 
of  these  conditions  are  found  in  the  phenocrysts  of  por- 
phyritic  rocks,  and  show  that  they  were  formed  under  the 
above  conditions.  » 

Primary  rocks  are  also  called  eruptive,  as  they  are  the 
result  of  a  continuous  process  from  the  original  earth-throe 
to  their  solidification  in  circumscribed  areas  into  which  they 
have  been  forced.  The  variations  in  texture,  structure,  and, 
according  to  Wadsworth  and  Iddings,  mineral  composition 
depend  on  the  rate  of  cooling.  The  two  authorities  named 
do  not  lay  much  stress  on  the  influence  of  pressure,  though 
others  do  so  to  a  great  extent,  and  divide  rocks  into  "  plu- 
tonic"  (abyssal,  abysmal,  etc.)  and  "volcanic,"  or  those 
formed  at  depths  and  at  the  surface.  All  porphyritic  states 
can  no  longer  be  taken  as  evidences  of  intratelluric  crystal- 
lization before  effusion,  as  the  researches  of  Judd,  Van  Hise, 
and  others  show  that  crystal-building  progresses  after  solid- 
ification, either  through  devitrification  or  through  out- 
growths about  crystals  or  grains,  as  some  quartz-porphyries 
are  found  to  be  devitrified  pitchstones.  It  will  require  the 
microscope  to  distinguish  between  original  and  secondary 
porphyritic  states.  Chemical  bulk  analyses  can  no  longer 
be  depended  upon  for  separation  of  species,  owing  to  the 
great  variation  in  the  values  of  the  elements  of  the  same 
mineralogical  combination,  and  the  high  agreement  between 
bulk  analyses  of  widely  varying  mineralogical  compounds. 
Some  of  the  states  formed  under  different  conditions  have 
been  already  described,  but  they  can  be  grouped  under  two 
main  heads,  dependent  on  whether  they  reached  the  surface 
or  not.  They  may  be  said  to  have  a  uniform  abyssal  ori- 
gin, but  we  know  them  as  eruptives.  If  they  were  forced 
towards  the  surface,  but  failed  to  reach  it,  they  were  intru- 
sives  ;  if  they  reached  it  and  were  effused  upon  it,  they  be- 
came extrusives.  The  former  are  distinguished  by  few  or  no 


g  MANUAL    OF  LITHOLOGY. 

gas-pores  (and  this  is  considered  a  result  of  pressure),  but 
possessing  miarolitic  structures  (which  are  thought  to  be  of 
similar  origin) ;  the  latter  are  rich  in  vesicular  states,  and 
other  evidences  of  a  release  of  pressure,  and  a  consequent 
escape  of  the  included  vapors.  Secondary  rocks  will  be 
discussed  later. 


PRIMARY  ROCKS. 

It  has  been  conclusively  proved  by  the  finding  of  rhyontes 
extending  from  the  present  to  pre-Cambrian  times,  and 
quartz-porphyries  forming  as  late  as  the  Eocene,  that  in  all 
geological  times  the  extrusions  have  been  of  the  same  char- 
acter ;  so  that  no  division  can  be  made  in  rocks  on  account 
of  geological  age.  Studies  in  Scotland,  where  high  moun- 
tains allow  the  same  mass  to  be  studied  at  different  eleva- 
tions, and  where  the  conditions  of  consolidation  were  dif- 
ferent, have  shown  us  deep-seated  rocks  running  into  what 
were  once  thought  to  be  different  forms  that  were  found 
only  at  the  surface.  The  cutting  of  the  Comstock  lode  by 
the  Sutro  tunnel  showed  the  same  on  a  grander  scale  ;  so 
that  the  old  terms  "  plutonic  "  and  "  volcanic  "  are  not  so  far 
apart  as  some  would  think.  In  the  present  treatise  the  old 
terms  are  put  aside,  as  all  extrusives  are  not  of  volcanic 
origin,  for  the  greater  bulk  of  surface  flows  came  from  dikes. 
The  terms  plutonic  and  abyssal  do  not  lay  enough  stress  on 
the  fact  of  motion  in  the  body,  as  most  of  the  rocks  have 
been  moved  from  their  places  of  liquefaction,  and  are  either 
thrust  into  or  through  openings  in  the  crust,  and  solidify  at 
various  depths  or  at  the  surface.  They  are,  as  before  stated, 
either  intrusive  or  extrusive,  and  the  later  statements  of  Id- 
dings  allow  us  to  be  careless  of  the  depth  at  which  rocks 
solidified,  as  that  had  little  to  do  with  their  mineral  com- 
position, which  depending  on  the  rate  of  cooling.  In  fine,  all 
rocks  are  closely  related  together,  and  in  the  following 


98  MANUAL    OF  LITHOLOGY. 

pages  instances  will  be  quoted  where  they  have  been  seen 
shading  from  one  species  to  another,  or  from  one  state  to 
another.  The  mineralogical  composition  of  rocks  is  taken 
as  the  basis  of  division,  and  of  these  minerals  only  those 
which  are  necessary  for  the  rock  species  are  meant.  These 
necessary  minerals  can  be  divided  into  six  groups,  as  fol- 
lows : 

(a)  The  black  bisilicates  (pyroxenes,  amphiboles,  micas), 
which  are  found  as  essential  ingredients  in  all  the  modern 
rock  systems. 

(b)  Quartz. 

(c)  Alkali  feldspars. 

(d)  Plagioclases. 

(e)  Feldspathoids  (nepheline,  leucite,  haiiyne,  melilite). 
(/)  Olivine. 

The  first  of  these  is  the  basis  for  classification,  and  the 
various  rocks  will  be  divided  as  they  contain  one  of  these 
groups  or  the  minerals  commonly  associated  with  them  ; 
thus,  granite  is  a  combination  of  mica  with  quartz  and  an 
alkali  feldspar.  Other  occurrences  of  mica  are  with  pre- 
dominant pyroxenes  or  amphiboles.  In  the  granite  group 
mica  js  predominant ;  but  the  term  "  granite  "  is  extended 
to  include  eruptives  of  predominant  quartz  with  a  small 
content  of  tourmaline,  or  predominant  feldspar  with  little 
quartz  or  mica.  In  the  same  way,  in  the  pyroxene  group, 
gabbro  consists  of  pyroxene,  plagioclase,  olivine,  and  mag- 
netite. Segregations  along  the  selvages  of  such  dikes 
show  rocks  that  are  little  more  than  aggregations  of  mag- 
netite ;  and  some  authorities  class  this  mineral  as  a  variety 
of  gabbro.  On  this  basis  the  mica  rocks  are  found  to  be 
the  most  acid,  and  the  mica  varieties  of  other  rock  groups 
carry  the  highest  silica  contents  ;  the  amphibole  rocks  are 
intermediate  in  both  mineralogical  and  chemical  constitu- 
ents ;  and  the  pyroxene  rocks  are  the  most  basic.  Olivine  is 


PRIMARY  ROCKS.  99 

the  antithesis  of  quartz,  and   each   is  important  where  the 
other  is  rare.     We  arrange  the  rocks  as : 

1.  Acid  (mica,  alkali  feldspar,  and  quartz). 
II.  Intermediate     (amphibole,     feldspar — subordinate 
quartz,  mica,  pyroxene,  feldspathoids,  and  olivine). 

III.  Basic  (pyroxenes,  plagioclases,  feldspathoids,  and 
olivine). 

For  the  purpose  of  general  description  rocks  can  be 
divided  into  various  combinations  of  the  above  minerals,  no 
matter  whether  those  were  formed  in  masses,  apophyses, 
dikes,  or  extruded  sheets.  The  conditions  found  in  dikes 
are  simulated  in  the  selvages  of  masses,  while  wide  dikes 
show  the  same  differentiations  in  texture  that  obtain  in 
masses  ;  and  as  many  of  the  distinctions  between  dike  and 
other  intrusive  states  depend  on  the  microscope,  these 
states  will  be  included  under  the  typical  combination,  with 
a  statement  that  they  are  otherwise  classed  by  some  author- 
ities. 

The  acid  rocks  will  have  above  66$  of  silica,  and  the  ultra- 
acid  a  great  content  of  free  quartz ;  their  color  is  generally 
light,  and  their  texture  frequently  compact-vitreous,  but 
seldom  amygdaloidal  in  structure.  The  intermediate  rocks 
are  generally  darker  in  color  than  the  acid,  with  higher 
specific  gravity,  a  greater  tendency  to  amygdaloidal  states, 
and  with  fewer  examples  of  vitreous-compact  textures. 
The  basic  rocks  are  dark,  with  high  specific  gravity,  few 
vitreous,  but  abundant  vesicular  and  amygdaloidal  states. 
In  general,  the  specific  gravity  and  percentages  of  soluble 
matter  in  rocks  are  inversely  proportionate  to  the  silica  con- 
tent. Acid  rocks  are  more  generally  distributed  over  the 
globe,  and  form  the  axes  of  the  great  mountain  ranges  and 
systems  ;  while  basic  rocks  are  local,  and  form  the  effusions 
of  isolated  volcanoes,  or  the  eruptions  through  fissures  of 
varying  extent. 


100  MANUAL    OF  LITHOLOG  Y. 

Recurring  to  the  two  main  divisions  of  extrusive  and 
intrusive  rocks,  we  can  distinguish  intrusive  rocks  as  more 
crystalline,  extrusive  as  more  compact ;  intrusives  as  lack- 
ing vesicular  states,  extrusives  as  abounding  in  them  ; 
intrusives  as  exhibiting  more  porphyries,  extrusives  more 
porphyritic  states  ;  intrusives  as  cooled  under  great  press- 
ure and  sometimes  with  great  slowness,  extrusives  as  cooled 
more  or  less  rapidly  and  under  little  pressure. 

As  an  example  of  the  association  of  rocks  in  a  group,  the 
rhyolite-granite  group  will  be  briefly  described  to  show 
the  method  followed  in  this  book.  Granite  is  a  coarse  crys- 
talline-granular (granitoid)  rock  (intrusive),  which  is  found 
in  large  bosses  which  are  frequently  fringed  by  apophyses 
into  the  surrounding  country-rocks.  The  cooling  effect  of 
the  country  increases  as  the  apophyses  narrow,  so  that  the 
granitic  filling  of  the  fissure  shows  a  gradual  diminution  in 
the  size  of  the  crystals  till  a  compact  texture  is  reached,  and 
this  changes  from  stony  to  vitreous  as  the  fissure-end  is  ap- 
proached. These  crystalline,  stony,  or  vitreous  states  may 
or  may  not  contain  phenocrysts,  and  thus  form  porphyritic 
states,  or  porphyries.  We  thus  find  "  granite  "  in  the  crys- 
talline state ;  "  granite-porphyry,"  if  microcrystalline  with 
phenocrysts ;  "  felsite,"  if  stony; "  quartz-porphyry,"  if  quartz- 
ophyric;  "  pitchstone,"  if  a  vitrophyre;  and  "  pitchstone-por- 
phyry,"  if  with  phenocrysts.  These  would  have  an  average 
chemical  composition  and  be  formed  under  pressure,  but  they 
would  vary  in  rapidity  of  cooling.  If  a  dike  ran  from  this 
granitic  magma  to  the  surface,  and  through  this  a  flow  of  fluid 
rock  were  forced  during  along  period,  and  sufficient  to  thor- 
oughly heat  the  dike-walls,  and  if  this  flow  should  cease, 
leaving  the  fissure  filled  with  molten  material,  and  we  could 
follow  it  from  below  to  the  surface,  we  should  find  the  filling 
to  be  granite  at  such  depths  that  the  original  heat  supple- 
mented by  that  received  through  the  flow  had  been  sufficient 


PRIMARY  ROCKS.  IOI 

to  heat  the  dike-walls  to,  or  nearly  to,  the  temperature  of  the 
fluid  filling,  so  that  cooling  could  proceed  slowly.  Passing- 
upward  through  the  depths,  we  should  arrive  at  points  where 
the  dike-walls  were  less  heated,  and  the  quicker  cooling 
would  form,  with  gradual  losses  of  heat,  granite-  and  quartz- 
porphyries  or  felsite,  while  the  portions  thrust  into  fissures 
radiating  from  the  dike,  and  formed  at  the  time  of  the  orig- 
inal fracture,  would  form  the  vitrophyres.  These  would  all 
be  at  points  so  far  below  the  surface  that  the  hydrostatic 
head  of  the  fluid  would  act  against  the  expanding  gases 
sufficiently  to  obliterate  vesicular  states,  or  (?)  the  gases 
might  escape  into  the  porous  dike-walls.  As  the  surface 
was  neared  and  the  pressure  lessened,  the  vesicular  states 
would  become  more  prominent ;  and  if  the  dike-walls  were 
sufficiently  hot,  or  if  the  flow  at  the  surface  were  sufficiently 
thick,  crystallization  would  take  place  under  conditions  of 
great  slowness  ;  but  the  greatly  lessened — if  not  almost  want 
of  —  pressure  would  allow  the  crystals  to  form  with  a 
trachytic  facies,  and  include  between  them  microscopic 
blow-holes.  A  more  rapid  rate  would  cause  the  mass  to 
solidify  with  a  rhyolitic  facies  ;  while  the  portions  forced 
into  crevices  near  the  surface  would  become  trachytic  pitch- 
stones,  rhyolitic  pitchstones,  etc.,  according  to  their  facies, 
and  the  surface  of  the  flow  would  show  states  of  perlite  and 
obsidian.  Under  this  theory  all  members  of  the  granite 
group  may  have  been  formed  at,  or  nearly  at,  the  same 
time  and  from  the  same  magma,  by  variations  in  cooling 
and  pressure,  and  all  of  the  group  are  equally  eruptive. 
According  to  their  depth  from  the  surface,  they  can  be 
separated  into  : 
A.  The  intrusive  states. 

C.  The  crystalline  textures. 

P.  The  microcystalline  to  compact  textures,  with  or  with- 
out phenocrysts,  and  non-vitreous. 


IO2  MANUAL    OF  LITHOLOG  Y. 

V.  The    compact-vitreous    textures,   with    or    without 
phenocrysts. 
E.  The  extrusive  states. 

C.,  P.,  and  V.  As  above. 

AC.  Granite,  porphyritic-granite. 

AP.  Granite-porphyry,  quartz-porphyry,  felsite. 

AV.  Pitchstone,  pitchstone-porphyry. 

EC.  Rhyolite. 

EP.  Porphyritic  states. 

EV.  Perlite,  obsidian,   pumice. 

As  the  extrusive  states  are  more  common  and  more 
readily  accessible,  they  will  be  first  treated  ;  but  the  groups 
will  be  named  after  both  extrusive  and  intrusive  states  for 
readiness  of  correlation  in  the  field — thus,  the  above  group 
will  be  styled  the  rhyolite-granite  group. 

It  may  be  well  to  again  call  attention  to  the  fact  that, 
in  general,  the  vitreous  states  of  a  given  rock  group  are 
more  acid  than  the  crystalline  states,  especially  if  an  in- 
tratelluric  crystallization  began  in  the  magma  before  erup- 
tion, as  the  more  basic  minerals  crystallize  first,  and  the 
magma  thus  becomes  more  and  more  acid  with  each  sue- 

c> 

ceeding  addition  to  the  phenocrysts ;  so  that  a  sudden  cool- 
ing would  show  a  vitreous  state  more  acid  than  the  original 
magma.  In  general,  the  extent  of  the  development  of  the 
vitreous  states  of  a  rock  is  proportional  to  its  acidity,  and 
in  the  ultra-acid  rocks  large  masses  have  a  glassy  habit, 
as  the  obsidian  cliff  in  the  Yellowstone  National  Park.  In 
basic  rocks  the  extent  of  the  vitreous  development  is  con- 
tracted, till  it  is  limited,  in  the  ultra-base  rocks,  to  a  thin 
lining  of  vesicular  cavities,  thin  selvages  in  contact  with 
the  country  rock  through  which  the  eruptive  was  forced, 
thin  crusts  on  the  surface  of  sheets  or  streams,  or,  finally, 
narrow  dikes  of  a  few  inches,  or  minute  apophyses.  There 
are  very  few  rock  groups  that  do  not  show  glassy  states 


PRIMARY  ROCKS.  1 03 

under  both  intrusive  and  extrusive  conditions ;  the  syenites 
alone  have  not  been  found  with  them.  Many  of  these  vitre- 
ous states  are  characteristic  and  quite  readily  distinguished  ; 
but  in  the  majority  of  cases  they  cannot  be  determined  by 
the  naked  eye,  and  even  chemical  and  microscopical  analyses 
fail  to  separate  certain  basic  forms,  when  separated  from 
the  accompanying  crystalline  states.  The  intrusive  vitro- 
phyres  can  generally  be  distinguished  from  their  extrusive 
neighbors  by  their  lower  density,  and  the  general  absence 
of  vesicular  structure.  In  general,  the  acid  varieties  are 
of  lighter  color  than  the  basic  ;  but  in  the  same  extrusive 
acid  state,  if  the  rock  be  compact,  the  more  rapid  the  cool- 
ing the  darker  the  color,  as  is  seen  in  the  case  of  furnace 
slags,  which  vary  from  a  blackish  gray  highly  vitreous 
rock  to  a  grayish  white  feebly  lustrous  state.  Many  vitro- 
phyres  have  lost  their  lustre  through  devitrification 
{see  p.  61). 

Extrusive  rocks  are  found  as  lava  streams  with  amygda- 
loidal,  vesicular,  scoriaceous,  columnar,  fluidal,  and  other 
structures.  These  may  have  issued  from  a  central  vent  in 
recurrent  streams,  as  in  a  volcano,  or  through  an  extended 
fissure  in  a  single  outpouring  which,  by  cooling,  closed  the 
fissure  permanentlv,  as  in  a  sheet  eruption.  Subsequent 
erosion  removed  the  scoriaceous  surface  and  reveals  the  fill- 
ing of  the  volcanic  vent  as  a  neck  or  plug,  and  of  the  sheet 
as  a  ridge  which  may  have  a  breadth  measured  by  inches 
or  rods,  and  a  length  up  to  hundreds  of  miles.  The  name 
•dike  is  given  to  this  denuded  filling  (from  its  shape),  and 
thence  to  the  whole  filling,  and  many  authorities  have  sepa- 
rated dike  and  volcanic  extrusions  on  the  score  that  ve- 
sicular states  were  wanting  in  dikes,  forgetting  that  the 
lapse  of  time  has  allowed  these  to  be  removed,  with  the 
original  surface,  by  denudation,  so  that  we  see  only  the 
filling  of  the  fissure  at  depths.  Extrusions  through  dikes 


IO4  MANUAL    OF  LITHOLOGY. 

and  plugs  are  therefore  old  ones.  The  rocks  of  this  class 
melt  at  varying  temperatures,  of  easy,  medium,  and  difficult 
fusibility,  which,  according  to  Barus,  are : 

2250°  F.  for  basalt  and  the  basic  rocks  ; 

2520°  F.    "  andesite  and  the  intermediate  rocks ;  and 

3100°  F.    "    trachyte  and  the  acid  rocks. 

It  has  been  found  that  basic  extrusions  are  very  fluid  ; 
spread  over  the  country  in  thin  sheets,  and  form  mountains 
of  low  angle  ;  while  the  acid  types  swell  into  lofty  and  cir- 
cumscribed hills  (puys,  mamelons)  or  form  cones  of  con- 
siderable angle.  Deformations  of  the  earth's  crust  accom- 
panied by  intruded  masses  produce  fractures  of  varying 
sizes  and  dimensions.  These  fractures  may  have 

(a)  Three  dimensions   of  considerable  and   comparable 
extent,  and  may  run 

1.  Across   stratification   planes    without  unduly  forcing 
apart  the  strata ; 

2.  Along  stratification  planes  on  either  side  of  a  fissure 
from  the  side  or  below,  and,  by  uplifting  the  overlying  beds, 
form  an  arch  that  may  be  ten  thousand  feet  in  height,  and 
of    comparatively    limited     area    along   the     stratification 
planes ;  or 

(b]  One  small  and  two  large  dimensions.     Fractures  of 
this  kind  generally  ramify  from  those  of  the  first  class,  and 
their  walls  may  : 

3.  Rapidly   approach    one   another   to   form  a   root   or 
wedge-shaped  opening;  or 

4.  Extend  parallel  to  one  another  indefinitely,  and  across 
or  parallel  to  bedding  planes. 

The  material  injected  into  these  will  form  in 

1.  An  irregular  body  that,  if  large,  will  cool  slowly  and, 
if  abyssal  and  under  pressure,  as  in  granite,  gabbro,  etc.,  will 
form  a  boss. 

2.  A  similar  body  that  will  of  necessity  cool  under  some- 


PRIMARY  ROCKS.  IOJ> 

what  less  pressure,  to  form  a  laccolite  (Gilbert),  or  the  modi- 
fied term  laccolith  (].  D.  Dana). 

3.  A  body  of  limited  extent,  which  is  generally  considered 
in  connection  with   the  body  from  which  it  is  an  offshoot. 
These   bodies  are  variously  named ;   but  the   fact   of   the 
association   just    given    makes   the   term    apophysis   (plural 
apophyses,  from   Greek  "  an  offshoot ")  most  applicable,  as 
"  vein  "  is  better  confined  to  fillings  of  fissures  crystallized 
from  aqueous  solutions. 

4.  A  sheetlike  body,  which  is  best  termed  a  sheet.     If  it 
runs  across  the  strata  and  appears  at  the  surface  as  a  con- 
siderable outflow,  the  surface   part   is   called   an    extrusive 
sheet ;   but  if  narrow,  a  lava  stream,  as  in  the  case  of  a  vol- 
cano.    The  intrusive  part  below   the  surface  is  variously 
named ;  if  nearly  vertical  and  across  the  strata,  it  forms  a 
dike ;  all  portions  parallel  to  the  strata   form  intruded  or 
bedded  sheets  or  sills  ;  and  where  the  filled  fissure  runs  alter- 
nately with  and  across  the  strata,  it  is  said  to  be  stepped. 
Some  authorities  restrict  the  term  "  sheet"  to  surface  flows, 
and   call   underground  portions  "  dikes  "  or  "  interbedded 
sheets,"  as   they   happen   to   cut   across   or   run   with   the 
strata. 

Owing  to  the  greater  extent  of  bounding  surface  to  a 
given  bulk  of  injected  matter  in  forms  of  the  third  and 
fourth  kind,  the  cooling  is  more  rapid  and  the  size  of  crystals 
smaller.  When  sheets  extend  from  deep-seated  bosses  to 
the  surface,  they  show  all  varieties  of  structure  between  in- 
trusive and  extrusive  rocks  in  the  same  mass.  The  boss 
shows  the  largest  crystals  towards  its  centre,  and  these  di- 
minish in  size  towards  the  walls,  but  not  to  a  great  extent 
if  those  walls  were  so  deeply  seated  as  to  be  within  a  region 
of  great  heat,  or  if  the  eruptive  material  had  been  forced 
through  the  cavity  and  its  fissures  long  enough  to  heat  the 
walls  to  a  great  depth.  The  cooler  the  walls  the  more 


106  MANUAL    OF  LITHOLOGY. 

rapid  the  crystallization,  until,  with  sudden  cooling1,  a  com- 
pact mass  is  formed  that  will  show  phenocrysts,  in  case 
crystallization  began  before  eruption,  and  will  be  called  a 
porphyry.  Where  pressure  began  to  disappear,  the  in- 
cluded gases  expanded  to  form  vesicles,  and  the  propor- 
tion of  these  increased  with  nearness  to  the  surface  where 
the  lava  was  blown  up  to  form  a  foamy,  slaggy  mass. 

The  primary  rocks,  as  just  stated,  are  grouped  in  three 
divisions,  as  they  have  mica,  hornblende,  or  pyroxene  as  a 
characteristic  component.  <  This  does  not  presuppose  that 
they  are  necessary  components  of  all  the  varieties  of  the  di- 
vision to  which  they  belong  ;  it  indicates  that  the  minerals 
grouped  with  it  are  found  more  frequently  combined  with  it 
than  with  either  of  the  other  two  black  bisilicate  groups. 
Each  division  is  composed  of  rock  series,  and  these  are  subdi- 
vided into  groups  which  may  have  in  combination  but  one  of 
the  necessary  minerals  of  the  division,  as  the  gabbro  series  with 
necessary  plagioclase,  feldspathoids,  pyroxene,  olivine,  and 
magnetite  embraces  groups  which  have  but  one  of  the 
above  as  a  necessary  component,  as  plagioclase  for  the 
anorthosites,  olivine  for  the  so-called  peridotites,  etc. 

The  following  skeleton  will  show  the  method  of  arrange- 
ment of  the  rocks  : 

ACID  DIVISION. 

MICA  :  Quartz,  alkali  feldspar,  plagioclase,  amphibole,  pyroxene, 
magnetite,  feldspathoids,  olivine. 

Extrusive,  Rhyolite  ;  Intrusive,  Granite. 
INTERMEDIATE  DIVISION. 

AMPHIBOLE:  Feldspar,  quartz,  mica,  pyroxene,  feldspathoids,  mag- 
netite, olivine. 

Extrusives,  Trachyte,  Phonolite,  Andesite. 
Intrusives,  Syenite,  Elseolite- syenite,  Diorite. 
BASIC  DIVISION. 

PYROXENE  :  Plagioclase,  feldspathoids,  olivine,  magnetite,  amphibole, 
mica,  orthoclase,  quartz. 


PRIMARY  ROCKS.  IO/ 

The  intermediate  and  basic  divisions  will  be  fully  ar- 
ranged before  the  rocks  they  comprise;  the  acid  division  is 
a  simple  one  and  fully  arranged  above.  In  the  following 
definitions  the  signs  (M)  and  (m)  will  be  used  as  stated  in 
the  introduction ;  (M)  referring  to  the  megascopic  appear- 
ance of  a  rock,  or  the  manner  of  its  appearance  as  viewed 
with  the  eye  or  a  lens,  and  (m)  to  the  same  as  seen  with  a 
microscope,  or  of  such  a  size  that  it  can  be  seen  only  with 
that  instrument. 


ACID   DIVISION— MICA   ROCKS. 

This  is  the  most  widely  spread  over  the  earth's  surface, 
and  in  the  greatest  abundance  ;  and  it  has  been  the  longest 
stadied  of  all  the  divisions.  It  comprises  but  one  series — 
that  of  rhyolite-granite ;  but  that  is  greater  in  bulk  than 
all  of  the  others  combined.  As  the  extrusives  are  the  sur- 
face forms,  they  will  be  treated  first. 

GROUP   I.      RHYOLITE-GRANITE. 

ACID    EXTRUSIVES. 
(Necessary  minerals :  Quartz  and  an  acid  feldspar.) 

I.  Rhyolite. 
II.  Rhyolite  Glass. 


IO8  MANUAL    OF  LITHOLOGY 

I.     RHYOLITE. 

RHYOLITE    (v.   Richthofen),   Liparite    (J.    Roth),. 

Quartz-trachyte  (J.  Roth). 

A  compact  (sometimes  cavernous  or  drusy)  groundmass 
containing  crystals  or  crystalline  grains  of  sanidine 
and  quartz.  The  latter  is  usually  (M),  but  invariably 
(m).  As  (M)  essentials  tridymite  and  magnesia-mica 
and  (m)  magnetite  are  frequent,  and  both  (Mm)  plagio- 
clase,  muscovite,  hornblende  (in  prisms),  bronzite,  hy- 
persthene,  and  augite  are  infrequent  or  rare.  As  (M) 
accessories  red  garnet  and  cordierite  appear  in  the 
mixture,  and  topaz,  spessartite,  and  fayalite  in  druses. 
Silica  75-82  ;  Gr.  2.4-2.6;  H.  5.5-6. 

Rhyolite  is  not  known  as  the  lava  of  an  active  volcano, 
but  it  is  abundant  in  beds  and  sheets,  and  in  plugs  and 
dikes.  It  is  extensively  developed  in  central,  southern,  and 
southeastern  Europe,  Great  Britain,  Iceland,  East  Indies, 
New  Zealand,  South  America,  and  extensively  in  the  west- 
ern part  of  North  America,  and  especially  of  the  United 
States.  A  great  development  of  devitrified  pre-Cambrian 
rhyolite  occurs  along  the  South  Mountain,  across  the  border- 
line of  Pennsylvania  and  Maryland.  (See  later  under 
"  Aporhyolite.") 

The  groundmass  when  compact  is  felsitic  (as  in  quartz- 
porphyries),  like  claystone,  hornstone,  porcelain,  and 
crockery-ware.  The  fracture  is  flinty,  splintery,  conchoidaL 
When  cavernous,  the  cells  or  cavities  are  sometimes  round, 
sometimes  narrow  and  parallel,  sometimes  large  and  ir- 
regular. The  cavities  are  sometimes  filled  with  chalcedonic 
material,  hornstone,  or  jasper;  sometimes  with  quartz  and 
amethyst,  as  well  as  the  minerals  noted  in  the  definition. 
The  structure  is  sometimes  plane-parallel  (schistose)  and 
sometimes  fluidal,  with  such  minute  divisions  that  each  is  no 


PRIMARY  ROCKS. 

thicker  than  a  sheet  of  paper.  The  colors  are  white,  yel- 
lowish white,  greenish  white,  pearl-gray,  reddish  white,  ash- 
gray,  reddish  yellow,  greenish  yellow,  pink,  and  brick-red. 
The  feel  is  usually  smooth,  but  sometimes  rough  and  harsh 
in  the  porous  states.  The  luster  is  usually  shining  and  semi- 
vitreous,  but  frequently  dull  and  earthy.  The  sanidine  is 
sometimes  5  cm.  long,  but  in  the  United  States  has  not  been 
reported  larger  than  3  mm.  The  much-fissured  and  frac- 
tured crystals  frequently  show  Carlsbad  twinning.  The 
plagioclases  are  of  frequent  appearance,  but  of  small  pro- 
portion in  the  mixture,  and  they  are  usually  more  or  less 
completely  kaolinized,  so  that  chemical  analyses  are  neces- 
sary to  distinguish  them.  The  quartz  occurs  in  crystals 
and  rounded  grains,  or  fragments  of  grains,  in  sharp  con- 
trast to  the  groundmass.  The  color  is  clear  smoke-gray  to 
black,  and  in  size  up  to  a  hazel-nut.  It  is  distinguished  (Zir- 
kel)  from  that  of  granite  by  glass  inclusions,  that  are  some- 
times i  mm.  thick,  and  by  the  absence  of  fluid  inclusions. 
The  quartz  of  quartz-porphyry  is  distinguished  from  the 
two  by  containing  both.  Many  rhyolites  show  no  (M) 
quartz,  and  it  seldom  appears  alone.  The  magnesia-mica 
is  biotite  and  frequently  occurs  in  small  quantities,  and  in 
many  rhyolites  it  is  the  most  conspicuous  mineral,  and  gen- 
erally abundant  in  American  types.  It  is  sometimes  chlori- 
tized.  The  black  bisilicates  are  seldom  plentiful,  and  only 
in  scattered  cases  (M}.  Hornblende  is  the  most  common, 
with  augite  and  rhombic  pyroxene  much  less  prominent 
either  (M)  or  (m).  Tridymite  is  abundant  in  the  rocks  of 
the  United  States,  and  frequently  (M)  in  druses  and  cavities, 
but  not  in  the  mixture.  Of  the  accessories,  garnet  i  mm., 
cordierite  1-3  mm.,  topaz  3-10  mm.,  spessartite  2.5  mm. 
to  i  cm.,  and  fayalite  i  mm.,  occur.  In  some  cases  the 
groundmass  is  full  of  spherulites,  which  cause  the  rock  to 
-appear  perlitic.  They  are  sometimes  5  mm.  in  diameter. 


IIO  MANUAL   OF  LITHOLOGY. 

(a)  Lithoidite  (v.  Richthofen).     A  compact  felsitic  ground- 
mass  with  hornstone  fracture;  hardness  of  feldspar  and  habit 
like  clay  stone;  generally  light-colored;  no  (M)  quartz,  and 
almost  none  (m),  so  that  its  greater  proportion  of  silica  alone 
separates   it   from    trachyte.      The    fresh    groundmass    is 
porcelain-like    with    conchoidal-splintery    fracture ;   luster 
waxy,  with  few  minerals  showing. 

(b)  Millstone-porphyry   (popular  name  in   Hungary).     A 
felsitic  groundmass,  like  claystone,  of  dark  grayish,  yellow- 
ish shades,  or  brick-red,  full  of  cells  or  cavities  filled  with 
chalcedony,  hornstone,  jasper,  quartz,  and  amethyst.    It  con- 
tains 70$  of  silica. 

(c)  Nevadite  (v.  Richthofen),  Granitoid  Rhyolite.     A  dif- 
ference of  opinion  exists  as  to  the  existence  of.  a  ground- 
mass.     Rosenbusch  describes  the  rock  as  lacking  one,  but 
Zirkel  calls  attention  to  the  fact  that  v.  Richthofen  noted  a 
small  proportion  in  his  definition.      There  are  thus  types 
called  nevadite  with  and  without  a  groundmass,  which,  at 
best,  is  of  small  proportion.     Nevadite  is  a  crystalline  ag- 
gregate of  quartz,  feldspar,   biotite,  and    hornblende   in   a 
limited  groundmass  of  similar  composition  with  a  micro- 
scopic or  amorphous  texture.     Hague  and  Iddings  report 
that  the  original  nevadite  of  v.  Richthofen  is  a  dacite,  but 
they  found  in  the  Great  Basin  a  rock  of  the  above  descrip- 
tion, and  Cross  found  the  same  at  Leadville. 

(d)  Liparite.     A  felsitic  and  porphyritic  rhyolite  with  a 
stony  groundmass,  and  bearing  to  rhyolite  the  same  relation 
that   felsite-porphyry   does   to  felsite.     Rosenbusch  distin- 
guishes sanidine  and  albite  liparites,  but  the  word  is  used 
more  in  the  sense  of  rhyolite. 

(e)  Soda-rhyolite.      From    Berkeley    Hills,   Cal.      Silica 
75.46 ;  Gr.  2.42. 

(/)  Aporhyolite  (Bascom).    A  name  given  by  Miss  Bascom 
to  devitrified  rhyolite.     It  occurs  in  extensive  masses  in  the 


PRIMARY  ROCKS.  Ill 

South  Mountain  of  Pennsylvania  and  Maryland,  and  has 
been  completely  recrystallized  to  form  a  mosaic.  These 
rocks  were  distinguished  by  the  late  G.  H.  Williams.  They 
are  pink,  and  retain  fluxion  structures  and  lithophysse  of 
large  (M)  dimensions.  Subsequent  action  has  sheared  them 
so  that  slaty  cleavage  has  developed. 

The  rhyolites  can  be  told  from  the  quartz-porphyries  by 
the  greater  luster  of  the  groundmass,  and  by  the  fewer  pheno- 
crysts ;  and  nevadite  can  be  distinguished  from  granite  by 
the  presence  of  a  groundmass,  and  by  the  rock  being  por- 
phyritic,  and  not  crystalline. 

II.     RHYOLITE   AND    TRACHYTE    GLASS. 

The  vitreous  states  of  the  rhyolites  cannot  very  well  be 
distinguished  by  the  microscope  from  similar  states  of  the 
trachytes  (Group  2,  with  necessary  alkali  feldspar  and  one 
of  the  black  bisilicates,  but  with  a  high  degree  of  acidity)  in 
hand  specimens.  Their  occurrence  is  by  far  more  prevalent 
with  the  more  acid  rhyolites  than  with  the  trachytes,  but, 
owing  to  the  similarity  of  the  states  of  these  rocks,  they  will 
be  described  together,  as  chemical  analyses  are  necessary  to 
distinguish  between  them.  We  unite,  therefore, 

Group  I.  Rhyolite-granite  (necessary  minerals  quartz 
and  an  alkali  feldspar) ; 

Group  2.  Trachyte-syenite  (necessary  minerals  an  al- 
kali feldspar  and  hornblende). 

PERLITE,    Pearlstone. 

A  matrix,  sometimes  glassy,  more  frequently  enamel-like, 
pearly,  or  greasy  on  a  fresh  fracture,  containing  many 
round  grains  of  a  concentric  or  shaly  structure. 

Silica   70-82;    water  0-4;     Gr.    2.3-2.4;    of   the 
spheroids,  2.37-2.54. 

The  color  is  mostly  pale  gray,  lavender-blue,  and  dark 


112  MANUAL    OF  LITHOLOG  Y. 

gray,  though  sometimes  yellowish  brown.  The  spherules 
vary  in  size  from  i  mm.  to  an  inch  in  diameter.  They 
are  probably  caused  by  contraction  in  the  cooling  mass,  as 
in  some  basalts.  They  are  sometimes  shelly  ;  sometimes  com- 
pact, and  sometimes  radially  striped.  Their  composition  is 
felsitic.  The  rock  frequently  contains  nests  and  cracks 
which  are  lined  or  filled  with  fire-opal,  precious  opal,  jasper, 
and  semi-opal. 

(a)  Porphyritic  Perlite,  showing,  with  the  spherules,  abun- 
dant phenocrysts  of  sanidine  and  plagioclase  (with  sometimes 
anorthoclase),  black  mica  in  sharply  defined  lustrous  folia, 
and  sometimes  pyroxene  and  hornblende.     Quartz  now  and 
then  occurs,  and  in  one  or  two  instances  hypersthene  and 
bronzite.     Occasionally  red  garnets  are  found. 

(b)  Obsidian-perlite.     This  is  a  state  when  the  dense  mass 
preponderates  and  the  spherules  are  not  abundant. 

(c)  Vesicular  Perlite.     Here  the  mass  is  more  or  less  ve- 
sicular, and  the  color  grows  lighter  with  the  percentage  of 
pores  till  it  becomes  snow-white.    In  this  mass  the  spherules 
are  sporadic. 

(d)  Tr  achy  tic  Perlite.     A  perlitic  glass  colored  from  light 
to  dark  or  greenish  gray,  with  sanidine,  plagioclase,  and 
biotite — at  times  hornblende  and  augite.     This  occurs  with 
trachyte  at  Cervetri,  near  Sasso,  Italy,  and  elsewhere.    The 
majority  of  the  perlites  are  states  of  rhyolite. 

These  rocks  are  found  with  the  rhyolites  abundantly  in 
the  Lipari  Islands,  in  Hungary,  New  Zealand,  Mexico,  and 
the  western  part  of  the  United  States.  They  occur  in  thick 
lava-streams  and  in  dikes.  A  variety  is 

Marekanite  (Herter).  A  velvet-black  mass  from  Mare- 
kanka,  Siberia,  with  abundant  small  glass  spherules  of 
smoke-gray  to  orange-brown  color,  and  great  transparency. 


PRIMARY  ROCKS.  113 

RHYOLITIC  PITCHSTONE. 

A  vitreous  or  semivitreous  compact  rhyolitic  glass  of 
high  acidity  and  varying  color,  with  greasy  or  pitchy 
luster,  and  invariably  containing  chemically  combined 
water. 

Silica  66-80;  water  3-10;  Gr.  2.2-2.4;  H.  5-6.5. 

Both  rhyolite  and  trachyte  are  accompanied  by  pitch- 
stones,  but,  as  the  greater  number  occur  with  rhyolite,  the 
assembled  specimens  are  placed  under  the  name  of  the  former. 
They  bear  to  them  the  same  relation  that  the  felsite  pitch- 
stones  do  to  the  quartz-  and  felsite-porphyries.  They  are 
found  at  Hlinik,  Hungary,  in  Italy,  the  Hebrides,  Iceland, 
Nevada,  Utah,  Mexico,  and  South  America.  They  are 
mainly  of  a  dirty  green,  dark-brown,  or  black  color,  and 
conchoidal  fracture.  Though  they  may  have  the  same  luster 
as  obsidian,  they  can  be  distinguished  from  it  by  their  con- 
tent of  water,  as  obsidian  does  not  carry  above  one  per  cent. 
They  commonly  show  (m)  phenocrysts  of  white  or  colorless 
feldspar  (sanidine  or  plagioclase),  and  sometimes  augite  and 
quartz.  Rarely  and  in  inconsiderable  amounts  they  show 
{m)  garnet,  biotite,  what  seems  to  be  anorthoclase,  pyrite, 
pyrrhotite,  and  gold.  They  melt  with  more  or  less  difficulty 
to  a  frothy  glass  or  a  grayish-greenish  enamel,  and  give 
water  in  the  closed  tube.  They  are  untouched  by  acids. 

(a)  Trachytic  Pitchstone-porphyry.     At  Eigg,  Hebrides.     A 
velvet-  to  violet-black,  very  slightly   lustrous  rock,  rich  in 
•sanidine  and  single  plagioclases  of  large  size,  prisms  and 
grains  of  augite,  and  particles  of   magnetite ;    also  pyrite 
(Italy)  and  olivine  (Gough's  Island).     Silica  61-71. 

(b)  Perlitic  Pitchstone.     From  Massai  Land,  South  Africa. 
A  glass  carrying  perlitic  spherules  with  (M)  quartz,  bluish 
grains  of  arfvedsonite,  and  (m)  sporadic  brown  hornblende 
and  feldspar. 


114  MANUAL    OF  LITHOLOGY. 

(c)  Pumiceous  Pitchstone.  All  pitchstones  of  this  group- 
show  (m)  an  abundance  of  minute  vesicles  from  the  expand- 
ing steam.  These  are  usually  drawn  out  from  the  flow  of 
the  mass,  and  occasionally  they  are  so  expanded  and  so 
abundant  as  to  form  a  pumice. 

RHYOLITIC   OBSIDIAN,  Volcanic  Glass. 
A  compact  glass  of  varying  color  and    luster,  of  high 
acidity,  and   with   content   of   chemically   combined 
water  never  more  than  one  per  cent. 

Silica  70-77  ;  Gr.  2.35-2.45  (average  2.4) ;  H.  6-7. 

Obsidian  is  a  volcanic  glass  and  forms  the  surface  of 
quickly  cooled  acid  lava-streams.  In  general,  the  thickness  of 
the  glassy  state  is  inconsiderable ;  rarely — as  at  Obsidian 
Clifi,  Yellowstone  Park — it  forms  a  rock  of  extensive  dimen- 
sions which  is  entirely  of  this  state.  It  is  found  less  fre- 
quently with  trachytic  than  rhyolitic  effusions.  In  the 
western  part  of  the  United  States  it  is  extensively  developed, 
also  in  Mexico,  and  the  natives  used  it  for  knives,  heads  for 
spears  and  arrows,  axes,  etc.,  some  of  which  have  been  found 
east  of  the  Mississippi.  In  its  compact  state  the  steam 
vesicles  are  not  abundant  (m)  in  the  average  specimens ; 
but  whenever  found  they  are  egg-shaped  or  drawn  out  to 
threadlike  openings,  with  the  longer  axes  parallel  to  the 
line  of  flow.  Fluxion -structures  are  common.  The  color 
in  the  transparent  varieties  is  generally  uniform,  but  streaks 
and  parallel  banded  varieties  are  common.  The  shades  are 
light  or  dark  gray,  green,  grayish  blue,  and  yellowish  brown. 
It  is  sometimes  almost  colorless,  and  sometimes  so  black  as 
to  be  translucent  only  on  thin  edges.  It  fuses  on  the  edges  of 
thin  splinters,  but  gives  no  water  in  the  closed  tube.  Its 
hardness  is  greater  than  that  of  basalt  glass. 

(a)  Typical  Obsidian.   A  clear,  transparent  glass,  free  from 
crystals  or  inclusions  of  any  kind.     It  is  found  on  the  edges 


PRIMARY  ROCKS.  11$ 

of   streams   as   thin   crusts,  in    Siberia,   Iceland,  and   New 
Zealand,  and  also  occurs  in  large  masses  as  above  stated. 

(b)  Porpliyritic  Obsidian.     An  obsidian  mass  carrying  (M) 
phenocrysts  of  sanidine,  plagioclase,  laminae  of  biotite,  augite, 
and  quartz,  or  some  of  them.     This  is  common  in  certain 
parts  of  the  mass. 

(c)  Spherophyric  Obsidian,  when   the  glassy  mass  carries 
colorless,  grayish  white,  yellowish,  bluish  waxy  spherulites 
of  more  or  less  radial  structure,  which  sometimes  have  a 
parallel  arrangement. 

(d)  Lithophysic  Obsidian,  when    the  spherulites  are   con- 
centric and  form  lithophysas  (p.  78).      They  are  generally 
rich  in  (in)  minerals,  sometimes  visible   with  the  lens,  as 
olivine,  fayalite,  quartz,  tridymite,  etc. 

(e)  Vesicular  Obsidian,  when  the  mass  contains   a  large 
proportion  of  vesicles,  so  as  to  make  a  slaggy   structure, 
with  stretched  and  parallel  arrangement.  This  is  transitional 
to  pumice. 

(/)  Trachytic  Obsidian.  This  is  found  on  the  surfaces  of 
trachytic  lavas  in  Italy,  the  Azores,  and  elsewhere.  It  is  a 
yellowish,  greenish,  brownish,  or  pitch-black  transparent 
glass  with  feldspar,  biotite,  and  much  augite.  Contains 
silica  60-63  ;  Gr.  2.44.  It  occurs  in  porphyritic,  pitchstone- 
like,  and  vesicular  states. 

(g)  Bottlestone  (Ger.  "Bouleillenstein")  Pseudochrysolite, 
Moldauite.  From  near  Moldauthein,  Bohemia,  and  else- 
where. This  is  held  by  varying  authorities  to  be  natural 
and  highly  siliceous  glass,  and,  on  the  other  hand,  to  be  an 
artificial  product.  Rutley  says  that  it  is  the  former.  It 
occurs  in  large  grains  and  spheres  of  transparent  glass  one 
inch  thick,  with  irregularly  distributed  steam  vesicles,  in 
sand  near  the  above  place,  also  in  tuffs.  Contains  silica 
82.70.  Similar  glasses  have  been  described  from  other 
localities,  with  silica  76-81,  and  Gr.  2.17-2.35.  The  break- 


Il6  MANUAL   OF  LITffOLOGY. 

ing  of  the  surface  vesicles  produces  a  pitted,  corrugated, 
and  wrinkled  surface. 

(h)  Obsidian  Bombs.  Clear  glass  without  phenocrysts  in 
shape  of  bombs,  from  Australia,  and  with  Gr.  2.41-2.52. 

PUMICE. 

A  highly  porous  and  frothy  state  of  rhyolitic  obsidian, 
of  light  colors,  whitish,  grayish,  yellowish,  greenish, 
but  seldom  blackish. 
Silica  73  ;  Gr.  2.37. 

This  is  the  surface  state  of  a  rhyolitic-trachytic  effusion, 
and  occurs  especially  developed  in  the  Azores,  Lipari  Isl- 
ands, Iceland,  Mexico,  and  South  America,  and  in  some  of  the 
western  States  of  the  Union.  To  a  smaller  extent  it  is  found 
on  all  surface  flows  of  undenuded  condition.  The  pores  are 
sometimes  caused  by  a  trachytic  structure  of  the  magma, 
but  more  commonly  by  the  steam  vesicles.  It  fuses  more 
readily  than  obsidian  before  the  blowpipe. 

(a)  Obsidian-pumice.  This  is  the  pumice  of  commerce, 
free  from  phenocrysts,  of  extremely  light  colors,  approach- 
ing white,  and  is  extensively  found  in  the  Lipari  Islands 
and  Iceland. 

(U)  Perlitic  Pumice.  In  this  rock  the  tendency  to  spheru- 
litic  structure  was  stopped  by  extrusion  to  the  surface.  The 
vesicles  are  extremely  stretched  and  parallel,  so  as  to  form 
only  threadlike  openings,  and  among  them  are  minute  per- 
litic  spheres,  as  well  as  phenocrysts  of  sanidine,  biotite,  and 
quartz.  This  is  quite  common  in  Hungary. 

(c)  Porphyritic  Pumice.     In  the  Eureka  district  in  Nevada, 
and  elsewhere,  the  foamy  mass  carries  (M)  and  (m)  pheno- 
crysts of  sanidine,  plagioclase,  biotite,  augite,  quartz,  mag- 
netite, and  sometimes  red  garnet.     In  some  cases  the  pores 
are  filled  with  opal. 

(d)  Trachytic  Pumice.     A  vitreous  foamy  mass,  coarse, 


PRIMARY  ROCKS.  II 7 

fibrous,  and  felty,  a  cross  between  a  typical  pumice  and  a 
crystalline  magma.  This  is  a  transition  between  obsidian 
pumice  and  the  porphyritic  state. 

(e)  Trachyte-pumice.  A  dark-colored  foamy  state  of 
trachyte-obsidian,  greenish  brown,  brown,  or  black,  with  62 
per  cent  of  silica.  It  occurs  in  Italy,  the  Azores,  New  Zea- 
land, Philippine  Islands,  Hungary,  and  in  small  exposures 
in  many  other  localities. 

GROUP   II.     GRANITE   (OESALPINUS). 

ACID  INTRUSIVES. 

(Necessary  minerals:  Quartz  and  an  alkali  feldspar.) 
This  group  is  compounded  of  the  above  necessary  min- 
erals, associated  with  the  more  acid  of  the  plagioclases ; 
sparingly  of  the  amphiboles,  and  still  more  sparingly  of 
the  pyroxenes.  With  these  are  combined  a  large  number 
of  accessories.  The  group  is  characterized  by  a  variety  of 
states,  dependent  on  varying  conditions  of  solidification, 
and,  as  granite  is  one  of  the  most  extensive  and  well-known 
rocks,  each  of  these  states  has  been  distinguished  by  a  spe- 
cial name.  There  is  no  region  of  the  globe  without  granite, 
and  in  each  it  is  similarly  situated  with  regard  to  other  for- 
mations, as  a  foundation,  where  seen,  upon  which  they  have 
been  deposited.  It  forms  the  axes  of  extensive  mountain 
systems,  as  bosses  and  laccoliths  intruded  into  later  rocks, 
and  as  dikes  and  apophyses  which  penetrate  other  rocks — 
even  older  granites.  They  afford  evidences  of  their  heated 
state  during  intrusion  by  the  extensive  metamorphism  of 
their  enveloping  country-rocks,  which  will  be  more  fully 
treated  Under  "  Metamorphic  Rocks."  Some  authorities 
class  metamorphic  granites  with  gneisses,  and  others  place 
the  gneisses  formed  from  squeezed  granites  with  them  as 
original  states.  In  this  work  all  rocks  that  have  lost  traces 


Il8  MANUAL    OF  LITHOLOGY. 

of  secondary  origin  will  be  treated  as  primary.  The  English 
authorities  are  more  disposed  to  treat  all  granites  as  erup- 
tive, while  a  large  number  of  American  authorities  place 
them  as  the  result  of  complete  metamorphism  ;  but  they 
have  been  thrust  into  cracks  and  cavities,  so  that  they  ex- 
hibit all  the  apophyses,  etc.,  of  eruptive  granite,  and  cannot 
be  told  from  it  in  hand  specimens.  As  solidifying  under 
pressure,  there  are  neither  vesicular  nor  amygdaloidal  states, 
though  some  authorities  think  that  miarolitic  structures 
represent  the  former.  It  occurs  usually  massive,  and  with 
thick  tabular-jointed  structure,  and  weathers  spheroidally  to 
form  a  kaolin,  more  or  less  colored  by  the  iron  from  the 
black  bisilicates,  which  contains  as  angular  grains  the  quartz 
content  of  the  original  rock  ;  or,  in  certain  loosely  cemented 
and  porous  varieties,  the  grains  separate  to  form  sand  that 
may  be  metamorphosed  to  form  arkose,  or  granitic  sandstone. 
It  has  already  been  stated  that  crystallization  in  the  orig- 
inal magma  originated  either  with  the  most  basic  of  the  min- 
eralogical  components  or,  when  one  composition  was  greatly 
in  excess,  with  the  predominant  compound.  In  acid  gran- 
ites the  quartz  is  one  of  the  first  crystallizations,  as  shown 
in  quartz-porphyry  (unless  this  state  is  formed  from  a  sub- 
sequent devitrification  and  crystallization  of  pitchstone,  as 
Judd  and  others  have  shown  that  crystallization  can  take 
place  in  solid  rocks).  In  the  average  granites  the  feldspar  is 
greatly  in  excess  and  forms  the  idiomorphic  component, 
while  in  the  basic  granites  the  black  bisilicates  are  first  crys- 
tallized. The  average  granite,  therefore,  shows  generally 
-well-crystallized  feldspar,  with  mica  following  next,  and 
quartz  last.  With  slow  cooling  the  crystals  touch  one  an- 
other on  all  sides,  and  the  quartz  keys  the  others  into  a  firm 
;mass,  with  "  granitic  habit,"  unlike  the  porous  and  open 
•"  trachytic "  texture  of  some  of  the  rhyolites,  where  the 
crystals  touch  one  another  only  at  one  or  two  points.  The 


PRIMARY  ROCKS. 

members  of  the  granite  group  are  named  according  to  the 
relative  time  when  and  the  suddenness  with  which  intratel- 
luric  crystallization  was  checked.  We  distinguish  : 

I.  The  entirely  crystalline  state  without  (or  with   few) 
phenocrysts,  and  with  no  base  of  any  sort.     Under  this  is : 

(a)  Entirely  crystalline  and  without  phenocrysts,  as  typ- 
ical granite. 

(ft)  The  same  with  phenocrysts,  as  porphyritic  granite. 

II.  The  subcrystalline  state,  which  is  caused  by  cooling 
rapid  enough  to  produce  a  varying  proportion  of  stony  (fel- 
sitic),  but  not  glassy,  base,  as : 

(a)  A  crystalline  groundmass  with    more   or    less  base, 
and  carrying  phenocrysts,  as  granite-porphyry. 

(b)  A  stone  (felsophyre)  groundmass  carrying  phenocrysts 
of  quartz  and  perhaps  of  other  minerals.     This  can  be  defined 
as  a"  quartzophyric  felsophyre  "  (Dana),  or  quartz-porphyry. 
When  the  phenocrysts  of  quartz  become  sporadic,  or  entirely 
disappear,  it  becomes 

(c)  A  felsophyre  with  phenocrysts  of  orthoclase  (ortho- 
phyre)  or  plagioclase  (plagiophyre),  and  with  little  or  no 
visible  quartz  or  felsite-porphyry. 

(d)  A  felsophyre  without  phenocrysts,  as  felsite. 

III.  The  vitrophyric  state  reached  by  a  cooling  rapid 
enough  to  form  glass,  as  : 

(a)  A  vitrophyre  with  phenocrysts  of  some  of  the  compo- 
nent minerals   and   spherules  of   felsite,  as  pitchstone-por- 
phyry. 

(b)  A   clear   vitrophyre   without  phenocrysts,  as  pitch- 
stone. 


I2O  MANUAL   OF  LITHOLOGY^ 

la.  GRANITE. 

A  coarse-  to  fine-grained  completely  crystalline  com- 
pound of  quartz  and  an  alkali  feldspar  (usually  ortho- 
clase,  often  microcline)  and  a  mica.  As  essentials, 
acid  plagioclase  (usually  oligoclase,  often  albite,  now 
and  then  andesine),  and  sometimes  hornblende  ;  rarely 
a  pyroxene. 

Silica  60-82  ;  Gr.  2.59-2.73. 

This  is  an  important  economic  rock  in  the  United  States, 
but  has  been  most  highly  developed  in  New  England, 
whence  over  one-half  of  the  output  for  1891  was  taken.  It 
is  found  wherever  the  Archaean  is  exposed.  The  uniformity 
of  its  grain  increases  with  its  fineness.  In  the  so-called 
"  giant  granite  "  the  ingredients  are  in  large  masses.  The 
medium-coarse  texture  is  so  peculiar  to  this  rock  that  it 
supplies  the  adjective  "  granitoid "  to  similar  textures  in 
other  mineral  combinations.  A  very  fine  texture  forms  a 
"  microgranite,"  as  in  the  states  found  in  dikes  and  apoph- 
yses,  which  are  both  of  fine  grain,  and,  as  in  quickly  cooled 
states,  of  higher  acidity  than  the  average.  The  quartz  in 
granite  is  in  angular  grains  with  greasy-vitreous  luster,  con- 
choidal  fracture,  and  grayish-white  to  light-gray  color.  It 
is  sometimes  light  blue,  dark  blue,  bluish  gray,  dark  red,  and 
smoky.  It  fills  the  interstices  between  the  other  minerals, 
as  it  was  the  last  to  crystallize  completely,  and  locks  them 
together.  It  frequently  occurs  crystal  in  double  pyramids, 
and  then,  contrary  to  its  habit,  is  idiomorphic  with  respect 
to  feldspar,  the  opposite  usually  being  the  case.  As  crystal 
it  is  sometimes  %  of  an  inch  in  size  in  ordinary  granite ; 
in  giant  granite  it  occurs  in  large  masses.  In  graphic 
granite  and  pegmatite  it  forms  thin  plates  along  certain  cleav- 
age-planes of  the  feldspar  (microcline).  It  is  not  affected  by 
weathering.  The  orthoclase  is  mostly  in  regular  crystalline 


PRIMARY  ROCKS.  121 

grains.  On  fresh  cleavages  it  shows  a  pearly  luster.  The 
color  is  usually  reddish  white,  flesh-red,  or  yellowish  white, 
infrequently  grayish  or  greenish  (amazonstone),  rarely  deep 
red,  reddish  gray,  grayish  blue.  When  very  fresh,  it  has  a 
luster  like  adularia,  rarely  like  sanidine.  Twinning  occurs 
generally  in  porphyritic  phenocrysts,  not  in  granitic  grains. 
It  twins  mostly  according  to  the  Carlsbad  law  (some  are 
five  inches  long)  also  that  of  Baveno.  It  weathers  to  mica, 
kaolin,  talc,  pyrophyllite,  and  epidote.  Microcline  occurs 
alone ;  intergrown  with  orthoclase ;  and  replacing  it  as  in 
pegmatite.  Microperthite  is  frequently  found  (m).  Mica 
is  either  in  thin  irregular  folia  or  hexagonal  tables,  and 
scattered  sporadically  through  the  mass,  except  along  the 
selvages  of  bosses  and  dikes,  where  it  sometimes  (from  press- 
ure, or  the  influence  of  the  cooling  surface)  has  its  planes 
arranged  parallel  to  the  walls  of  the  country-rock  to  form  a 
schistoid  structure.  It  also  occurs  in  spherical  and  len- 
ticular concretions.  While  muscovite  and  biotite  are  gen- 
erally separate  from  one  another,  they  are  sometimes  found 
(Rosenbusch)  in  the  same  folia,  one  being  the  rim  to  the 
other,  or  in  the  same  tabular  crystal,  where  they  form  alter- 
nate folia,  so  that  optical  tests  are  necessary  to  distinguish 
between  them.  In  general,  biotite  predominates  over  musco- 
vite in  amount  and  in  regularity  of  crystallization.  Biotite 
is  the  more  basic,  and  in  varieties  of  average  composition  is 
the  earliest  crystallization  of  those  already  named,  and  this 
accounts  for  its  greater  regularity  of  form.  It  is  usually 
dark  brown  to  iron-black,  and  seldom  greenish.  Lepidome- 
lane  also  occurs  in  black  folia,  often  of  large  size.  Zinnwald- 
ite  is  found  in  tin-bearing  granites  (greisen)  in  black  folia, 
brown  to  brownish  red  by  transmitted  light.  Muscovite  is 
more  irregular  in  its  habit  than  biotite  and  crystallizes  after 
it,  but  usually  before  the  feldspars.  It  occurs  in  folia  and 
rhombic  tables.  Lepidolite  rarely  occurs  in  ordinary  gran- 


122  MANUAL    OF  LITHOLOGY. 

ite.  Rosenbusch  describes  it  as  the  mica  in  pegmatite. 
Of  the  essentials,  oligoclase  occurs  in  tabular  crystals  which 
are  generally  idiomorphic  with  respect  to  orthoclase  and 
quartz.  It  is  less  transparent  than  the  former.  To  a  small 
extent  it  forms  pegmatitic  structures  with  quartz.  Albite 
and  andesine  occur  now  and  then  in  the  more  basic  granites, 
and  labradorite  has  been  reported  in  one  case.  Plagioclase 
is  found  more  abundant  in  the  granitites  (biotite-,  hornblende-, 
and  augite-granites).  Hornblende  usually  crystallizes  in 
long  regular  prisms  with  irregular  terminations.  It  some- 
times has  a  uralitic  habit.  Augite  is  not  common,  and  then 
(m)  in  long  thin  prisms  or  crystalline  grains.  Light  yellow- 
ish brown  bronzite  occurs  in  rare  cases.  Calcite  some- 
times occurs  in  what  seems  to  be  a  primary  crystalli- 
zation; but  more  generally  it  is  a  secondary  product  in 
the  so-called  "kalkgranit."  In  rare  cases  altered  olivine 
occurs  (m). 

To  ascertain  which  minerals  are  idiomorphic  to  others 
it  is  only  necessary  to  remember  that  crystallization  proceeds 
from  basic  to  acid.  In  granite  the  principal  necessary,  es- 
sential, and  accessory  minerals  can  be  arranged  as  follows  : 
zircon,  apatite,  magnetite,  specular  hematite,  iimenite,  bio- 
tite, pyroxene  (usually  an  alkali  variety),  hornblende,  lepido- 
lite,  muscovite,  the  lime-soda  plagioclases,  albite,  orthoclase, 
microcline,  quartz. 

In  the  Brocken  granite  shades  into  gabbro  in  a  narrow 
zone  through  augite-biotite-granite,  augite-diorite,  diorite, 
and  quartz-biotite-augite-gabbro.  In  Skye  some  frag- 
ments of  porphyritic  hornblende-granitite,  included  in  a 
later  gabbro,  have  been  heated  so  that  the  granophyre  be- 
tween the  phenocrysts  has  been  changed  to  rhyolite  glass 
full  of  flow-lines,  spherulites,  lithophysae,  etc.  In  Sweden 
Nordenskiold  reports  that  halleflinta  is  a  devitrified  rhyolite 
that  shades  into  aplite,  and  that  into  granite. 


PRIMARY  ROCKS.  123 

The  (M)  accessories  in  the  United  States  include  the  fol- 
lowing species  anjd  the  following  localities  :  Maine :  Paris — 
tourmaline  ;  Readfield — andalusite.  Massachusetts  :  Chester 
— spodumene  ;  Chesterfield — cassiterite  ;  Greenfield — colum- 
bite  ;  Gloucester — danalite  ;  New  Bedford — molybdenite  ; 
Goshen — cassiterite,  tourmaline;  Connecticut:  Haddam — 
-anthophyllite,  allanite,  chrysoberyl,  columbite,  gahnite, 
garnet,  zircon  ;  Middletown — columbite  ;  Trumbull — topaz. 
New  York  :  Greenfield — apatite;  Warwick — rutile.  In  ad- 
dition to  the  above  there  are  found  in  foreign  localities  cor- 
dierite,  fluorite,  graphite,  native  gold,  pyrite,  specular  iron, 
allanite,  chlorite,  and  hydromica.  Granites  also  carry  con- 
cretions of  varying  size  and  composed  of-  various  mixtures 
of  the  components.  The  granite  group  embraces  the  fol- 
lowing varieties : 

(a)  GRANITE   (Muscovite-biotite-granite,  "  Eigent- 
licher  Granit "  of  Rosenbusch — not  of  G.  Rose  ; 
"  Zweiglimmeriger  Granit  "  of  Zirkel). 
A  granite  composed  of  quartz,  orthoclase,  more  or  less 
plagioclase,  and  both  muscovite  and  biotite  in  about 
equal  amounts. 

With  predominating  muscovite  or  biotite  it  passes  into 
those  varieties.  Hornblende  is  rare  and  pyroxene  absent, 
garnet  abounds,  and  cordierite  occurs.  It  is  coarse-  to  fine- 
grained and  porphyritic.  This  variety  is  the  great  moun- 
tain-former, but  also  occurs  in  bosses  and  dikes.  It  is  found 
in  Germany,  the  Vosges,  France,  extensively  in  Cornwall 
and  other  parts  of  Great  Britain,  Spain,  Mexico,  and  in  New 
England.  Rosenbusch  places  here  the  occurrences  with 
tourmaline,  while  Zirkel  puts  them  under  biotite-granite 
{granitite).  The  former  states  that  tourmaline  has  been 
formed  at  the  expense  of  biotite.  As  muscovite-granites  are 
rich  in  tourmaline,  garnet,  topaz,  cassiterite,  etc.,  and  as  the 


124  MANUAL    OF  LITHOLOGY. 

tourmaline  rocks,  etc.,  are  drusy,  they  will  be  placed  under 
muscovite-granite. 

(b)  MUSCOVITE-granite  (Rosenbusch). 
A  granite  composed  of  quartz,  orthoclase,  some  plagio- 
clase,  and  muscovite. 
Silica  75. 

This  is  the  most  acid  of  the  varieties ;  the  richest  in  quartz, 
and  the  poorest  in  basic  silicates,  magnetite,  etc.  It  occurs 
less  frequently  in  dikes  than  the  other  varieties.  Biotite 
may  occur  to  a  small  extent.  It  runs  to  extremes  in  texture, 
either  fine-grained  or  very  coarse.  It  is  frequently  drusy, 
but  porphyritic  states  are  rare.  It  is  rich  in  accessory  min- 
erals, especially  tourmaline,  garnet,  topaz,  cassiterite,  etc., 
and  is  found  extensively  in  Europe,  throughout  New  Eng- 
land, and  in  the  western  States.  Here  may  be  placed  : 

I.  Pegmatite  (Hauy)  Graphic  Granite.  A  compound  of 
reddish  feldspar,  quartz  of  dark  color,  and  silver-white  mica, 
so  arranged  that  the  rock  consists  almost  entirely  of  the  for- 
mer, which  is  pierced  along  certain  cleavage-planes  by  the 
quartz  so  as  to  produce  figures  similar  to  Assyrian  or 
Hebrew  letters.  The  mica  is  in  aggregates,  or  arranged 
parallel  to  the  quartz  tables,  and  frequently  coating  them. 
A  coarse  texture  forms  pegmatite,  a  fine  one  graphic  granite. 
Both  form  dikes  and  subordinate  masses  in  granite,  and  dikes 
and  interbedded  intrusives  in  metamorphic  schists.  They 
are  of  limited  extent,  are  associated  with  an  abundance  of 
accessory  minerals  given  above,  and  contain  78  per  cent  of 
silica.  According  to  the  best  authorities,  the  feldspar  is  mi- 
crocline  and  the  mica  lepidolite.  V.Cotta  calls  the  granites 
rich  in  feldspar,  which  have  their  content  of  mica  arranged  in 
stripes  or  branching  as  flower-stalks,  blumengranit  (Ger.). 
It  occurs  in  Germany,  France,  Sweden,  and  Normandy. 


PRIMARY  ROCKS.  12$ 

2.  Aplite,  Granitell,  (Ger.  "Halbgranit").    A  dike-granite 
of  uniformly  fine  grain,  composed  of  quartz,  orthoclase,  and 
some  plagioclase,  generally  without  mica,  or  with  a   very 
small  amount  of  silver-white  or  greenish  potash-mica.     It 
occurs  mostly  in  dikes,  but  in  one  or  two  cases  it  is  wide- 
spread.    The  localities  of  the  typical  rock  are  few.     It  is 
found  in  Hungary,  the  Vosges,  Germany  east  of  the  Rhine, 
in    South   Africa  (with   calcite).     It  is  distinguished   from 
granulite  by  its  want  of  schistose  structure  and  the  absence 
of  metamorphic  minerals,  especially  garnet.     According  to 
the  later  differentiation   theories,  this  is  the  "  complemen- 
tary "   rock   to   minette   from   a  granitic    magma.     In    the 
Melibocus  a  dike  runs  from  the  gneiss  on  the  east  side  to 
the  granite  on  the  west  side.     The  filling  in  the  gneiss  is 
rnicaless  aplite  ;  in  the  granite,  aisbachite,  a  highly  micaceous 
.granite-porphyry. 

3.  Cordierite-granite.     A  rock  of  limited  occurrence  in 
Norway,  Greenland,  Bavaria,  Australia,  in  which  cordierite 
(iolite)  is  abundant  and  mica  scarce.     Gr.  2.6-2.7. 

Here  follow  a  series  of  rocks  formed  during  granitic 
eruptions  through  the  influence  of  what  the  French  authori- 
ties call  "  mineralizing  agencies."  These  are  the  gases 
accompanying  the  ascent  of  the  magma,  and  which  some 
authorities  think  were  absorbed  during  the  cooling  of  the 
earth  from  a  nebulous  to  a  fluid  state,  and  which  are  included 
in  all  magmas.  Acid  magmas  are  supposed  to  possess  them 
to  a  high  degree  ;  some  authorities  would  substitute  the 
word  "  retain  "  for  "  possess,"  as  acid  magmas  are  less  fluid 
at  the  time  of  eruption  and  gases  can  less  readily  escape 
from  them  than  from  those  more  basic  and  fluid.  The  "  min- 
eralizers  "  are  aqueous  vapor,  fluorine,  boric  acid,  and  other 
volatile  acids — the  ones  acting  on  the  following  rocks  being 
those  named.  These  in  their  effort  to  escape  leave  the 


126  MANUAL    OF  LITHOLOG  Y. 

greater  part  of  the  magma,  but  are  entangled  in  other  por- 
tions (according  to  one  view) ;  or  they  are  forced  into  the 
still  molten  mass  along  lines  of  greater  fluidity  (according 
to  another  view),  and  form  new  compounds,  some  of  which 
are  pseudomorphs  after  the  original  minerals,  such  as  tour- 
maline, topaz,  cassiterite,  lepidolite,  zinnwaldite,  fluorite,  etc. 
These  rocks  are  : 

4.  Tourmaline-granite.  A  granitoid  compound  of  ortho- 
clase,  quartz,  and  tourmaline,  with  little  or  no  muscovite. 
Gr.  2.6-2.9.  Here  tourmaline  replaces  biotite  (Rosenbusch).. 
It  occurs  in  Saxony,  at  Predazzo,  Italy  (in  typical  form), 
near  Eisenach,  Hungary,  at  the  Eibenstock  (where  the 
tourmaline  is  frequently  in  masses  as  large  as  the  head),  ira 
Bohemia,  near  Heidelberg,  in  the  Tyrol,  Spain,  etc.  Tour- 
maline-bearing muscovite-granites  are  found  in  the  Vosges. 
extensively,  and  elsewhere.  In  some  instances  they  are 
pegmatitic,  and  with  tourmaline  one  foot  long.  The  other 
tourmaline  compounds  will  be  placed  here  to  group  them 
in  a  compact  body,  though  they  may  fall  under  other  varie- 
ties of  granite. 

(a)  Luxullianite  (Pisani).     This  is  named  from  the  parish 
of   Luxullyon,  Cornwall,  where    the    rock   occurs  in  loose 
blocks  (not  massive).     It  is  a  dark  mass  composed  (m)  of 
a  quartz  ground  filled  with  hairlike  tourmalines,  and  carry- 
ing large  grains  of  the  same,  small  orthoclases,  and  beautiful 
large  phenocrysts  of  the  same,  of  yellowish-red  color,  twa 
inches  in  size,  and  flecked  with  spots  of  tourmaline.     The 
tourmaline  is  said  to  be  an  altered  zinnwaldite. 

(b)  Trowlesworthite  (Bonney).     Another  Cornish  granitic 
compound  of  reddish  orthoclase,  acicular  tourmaline,  purple- 
red  fluorite,  and  scanty  quartz.     The  fluorite  has  replaced 
the  quartz  so  as  .to  form  one-fifth  of  the  whole  mass. 

(c)  Hyalotourmalithe  (Daubr£e),  Carvoeira  (von  Eschwege), 


PRIMARY  ROCKS. 

Tourmaline-quartzite,  Tourmaline  Rock.  These  are  names  of 
two  extremes  in  composition  of  a  Cornish  granitic  segre- 
gation which  has  been  formed,  through  the  entrance  into 
the  body  of  the  mass,  and  not  along  its  selvages,  of  fluoric 
or  boric  ingredients  as  exhalations.  The  tourmaline  has 
grown  at  the  expense  of  the  feldspar  and  mica.  In  some 
cases  there  is  a  small  amount  of  orthoclase  in  the  mass  or  in 
the  many  drusy  cavities.  The  mixture  of  black  tourmaline 
(blue  or  brown  by  transmitted  light)  and  quartz  as  a  granu- 
lar compound  is  the  "  tourmaline-quartzite,"  while  the  aggre- 
gate of  tourmaline  with  little  or  no  quartz  is  the  "  tourmaline 
rock."  "  Carvoeira  "  is  the  name  given  to  a  similar  rock  in 
Brazil. 

5.  TOPAZ  ROCK,  Topazfels  (Werner),  Topazosfcme 

(Brongniart). 

A  usually  granitoid  rock  which  is  sometimes  (owing  to 
the  age  of  its  formation)  greatly  decomposed  by 
weathering.  It  is  composed  of  predominant  topaz 
(which  sometimes  forms  90  per  cent  of  the  mass),  with 
quartz,  mica' (frequently  zinnwaldite),  cassiterite,  tour- 
maline, sphalerite,  and  fluorite. 

The  first  noted  occurrence  of  the  rock  was  at  the 
Schneckenstein  in  the  Voigtland,  where  a  dike  of  tourmaline 
rock  has  broken  through  phyllite  and  formed  a  breccia. 
Both  phyllites  and  breccia  are  impregnated  with  topaz. 
In  this  case  it  is  a  secondary  rock,  but  it  occurs  at  the 
Eibenstock,  Markersbach,  and  elsewhere  as  a  regular  crys- 
talline primary  rock,  and  is,  therefore,  placed  here  rather 
than  among  the  secondary  rocks. 


128  MANUAL    OF  LIT  HO  LOG  Y. 

6.  GREISEN  (Old    German  mining  name),  Hyalo- 
micte  (Brongniart). 

A  grayish  granitoid  compound  of  light-gray  quartz  and 
a  grayish,  yellowish,  or  greenish  mica  (zinnwaldite). 
Silica  80. 

This  is  another  granite  without  feldspar,  as  the  exhala- 
tions have  replaced  this  and  other  minerals,  so  that  quartz 
is  found  pseudomorphed  after  feldspar  (which  is  sometimes 
twinned)  and  mica,  while  cassiterite  forms  pseudomorphs 
after  feldspar,  similarly  twinned  in  some  cases.  It  is  of 
limited  extent  and  is  valuable  as  the  gangue  of  cassiterite. 
It  resembles  granite  in  its  irregular  jointing,  and  is  associated 
with  it  in  strings  and  pockets.  Scattered  through  it  are 
cassiterite,  fluorite,  tourmaline,  and  topaz.  It  is  found  in 
Saxony,  Cornwall,  and  the  Black  Hills,  S.  Dak.  When 
cassiterite  is  uniformly  scattered  through  the  rock,  it  forms 
/z«-granite. 

7.  ZWITTER  ROCK. 

A  medium-  to  fine-granitoid,  dark-green  (or  gray)  com 
pound  of   (M)  quartz,  with   smaller   topaz   and   cas- 
siterite, with  or  without  (m)  potash-iron  mica. 
Quartz  50-70$. 

This  is  the  gangue  of  the  tin  ore  of  Altenberg,  Saxony, 
called"  zwitter."  The  quartz  is  all  that  can  be  detected 
by  the  naked  eye,  the  other  ingredients  being  visible  only 
through  the  lens.  With  this  are  associated  mispickel,  mica- 
ceous hematite,  and  chlorite. 

8.  Epidote-granite,  Unakite.  A  granite  with  epidote 
abundant.  It  is  an  altered  granite,  the  epidote  coming  from 
the  black  bisilicates,  mica,  or  hornblende  (sometimes  feld- 
spar). It  is  found  in  the  Fichtelgebirge,  Schwarzwaid, 


PRIMARY  ROCKS. 

Pyrenees.  In  the  United  States  a  variety  with  flesh-red  feld- 
spar, quartz,  and  epidote,  from  the  Unaka  Mountains,  N.  Y., 
and  from  Tennessee,  is  called  unakite. 

(c)  GRANITITE  (G.  Rose),  Biotite-granite. 
A  basic  granite  composed  of  quartz,  red  orthoclase,  pla- 
gioclase,  and  magnesia-mica  (biotite). 
Silica  67-70. 

This  is  the  most  widely  disseminated  variety  of  granite. 
It  occurs  in  bosses  and  dikes,  is  denser  than  the  muscovite 
variety,  and  does  not,  like  it,  contain  drusy  cavities.  It 
abounds  in  porphyritic  states  and  in  plagioclase,  and  (as 
shown  in  the  silica  content)  is  poorer  in  quartz  than  any  of 
the  other  varieties.  As  a  basic  variety  it  is  richer  in  horn- 
blende as  essential,  and,  by  its  increase,  shades  into  horn- 
blende-granite. In  this  case  there  is  a  diminution  in  or- 
thoclase, and  a  still  further  loss  of  quartz,  so  that  the  excess- 
ive reduction  of  these  two  components  causes  it  to  shade 
into  quartz-diorite  and  diorite.  As  the  muscovite-granites 
are  rich  in  essential  tourmaline  and  quartz,  these  basic  gran- 
ites are  free  from  the  former,  and  almost  free  from  garnet 
-and  iolite  (cordierite)  ;  but  magnetite  and  specular  hematite 
are  higher  than  in  other  granites.  It  is  found  in  Germany, 
Bohemia,  Tyrol,  Alsace,  Italy,  Corsica,  Great  Britain,  widely 
spread  in  Sweden,  in  Greenland,  China,  Australia,  the  west- 
ern continent,  and  especially  western  North  America.  A 
small  amount  of  hornblende  and  augite  causes  varieties  that 
take  those  minerals  as  adjectives,  as  hornblende-grzmtite, 


I.  Kalkgranit  (Pichler),  Lime-granite.  From  the  Flag- 
gerthal  in  the  Tyrol.  A  granitoid  compound  of  quartz, 
biotite,  dark-green  chlorite,  reddish  orthoclase,  white  plagio- 
clase, and  transparent  particles  of  calcite.  Granites  with 


130  MANUAL    OF  LITHOLOGY. 

calcite  occur  in  the  Odenwald  and  in  Sweden,  and  Hawes 
found  it  at  Columbia,  N.  H.  While  some  authorities  find 
that  calcite  is  an  infiltration  product,  others  see  in  it  a 
primary  generation. 

2.  Hornblende-granitite  (Rosenbusch).     A  granite  with 
an  equal  amount  of  hornblende  and  biotite.     These  granites 
occur  in  the  Scottish  Highlands,  Saxony,  Alsace,  the  Oden- 
wald, Fichtelgebirge,  the  Channel  Islands,  Scandinavia,  the 
Troad,  and,  in  the  United  States,  in  the  Wasatch,  Shoshone, 
and  Havillah  mountains,  at  the  famous  quarry  at  Quincy, 
Mass.,  and  in  Minnesota. 

(a)  Kammgranite  (Groth).     A  porphyritic  variety  much 
developed  in  dikes  in  the  Vosges,  with  silica  62. 

(b)  Rapakivi  (Finnish  local  name).      A  "  rotten  stone  "- 
hence  the  name — extensively  distributed  near  Wiborg,  Fin- 
land.    A  coarse-grained  aggregate  of  egg-shaped  orthoclase 
(never  crystalline)  up  to  two  inches  in  length,  of  brownish- 
red  color,  and  covered  with  a  scaly  shell  of  oligoclase,  lepi- 
domelane,  and  hornblende,  and  generally  of  two  or  more 
colors.     The  darker  has  irregular  dark-gray  quartz  scattered 
through  it ;  the  lighter  and  weathered  state  has  the  quartz 
more  crystalline  and  the  feldspar  more  weathered.     Silica 
70.     The  high  silica  content  is  due  to  the  leaching  of  the 
alkalies. 

(c)  Granio-diorite  (Becker).      A  granite  poor  in   potash, 
with    predominant    plagioclase,    orthoclase,    quartz,    horn- 
blende, and  brown  mica.     With  orthoclase  in  excess  it  is  a 
hornblende-granitite ;  with  little  orthoclase,  it  is  a  quartz- 
mica-diorite.     Silica  60.     It  is  the   rock   of   the  Yosemite 
Valley. 

3.  Augite-granitite  (Rosenbusch),  Pyroxene-biotite-gran- 
ite.     A  granitite  with  usually  monoclinic  pyroxene  (augite). 
The  localities  are  noted  below  under  the  varieties. 

(a)  Gabbro- granite     (Tornebohm).      From     Haakanbols, 


PRIMARY  ROCKS. 

Sweden,  where  it  is  composed  of  gray  plagioclase,  ortho- 
clase,  brown  mica,  green  diallage  (or  a  diallage-like  augite), 
hornblende,  and  quartz.  As  accessories  are  titanite,  mag- 
netite, and  apatite. 

(b)  Augite-gramte.   A  gabbro-like  granite,  with  monoclinic 
augite,  rich  in  plagioclase  and  biotite.     The  pyroxene  in  all 
these  varieties  is  the    idiomorphic    mineral.     It  occurs  in 
England,  Labrador,  the  Vosges,  etc.,  and  the  augite  is  fre- 
quently uralitized. 

(c)  Augite-soda-gramte.  A  red,  drusy,  fine-grained  granite, 
sprinkled  with  dark  spots.     It  is   composed  of  orthoclase, 
anorthoclase,  quartz,  and  augite,  with  accessory  hornblende, 
biotite,  apatite,  sphene,  and  secondary  chlorite.     Silica  66-72. 
This  is  said  to  be  one  of  those  very  infrequent  occurrences 
— an  alteration  product  of  a  sediment  as  it  occurs  between 
eruptive  gabbro  and   slate.     It  is  reported  from  St.  John, 
N.  B.,  and  Minnesota. 

(d)  HORNBLENDE-GRANITE  (Naumann),  Sye- 
nitic  Granite  (v.  Cotta),  Syenite  (in  part,  of  G. 
Rose). 

A  granite  usually  poor  in  quartz,  with  little  or  no  mus- 
covite,  but  generally  containing  biotite,  orthoclase 
(and  sometimes  red  microcline),  plagioclase,  and  horn- 
blende. 

Silica  71.78. 

It  occurs  in  bosses,  dikes,  and  widely  distributed  masses 
in  Saxony,  Bohemia,  Austria,  Sweden,  Finland,  Pyrenees, 
France,  Great  Britain,  Greece,  Mount  Sinai,  Egypt,  Altai 
Mountains,  and  in  the  United  States  in  Minnesota,  Nevada, 
and  Canada.  The  quartz  is  variable  from  abundant  to 
rare.  In  the  former  case  biotite  fails.  Plagioclase  is  more 
abundant  than  in  biotite-granite  (granitite).  Orthoclase 
varies  in  color  from  light  to  deep  red ;  plagioclase  is  usually 


132  MANUAL    OF  LITHOLOGY. 

white.  Hornblende  is  in  green  crystals  (sometimes  over  an 
inch  long)  and  sometimes  appears  uralitized.  Titanite  and 
apatite,  malakolite  (or  a  diallage-like  augite)  and  rhombic 
pyroxene,  are  accessories.  It  is  frequently  porphyritic  from 
large  phenocrysts  of  orthoclase.  Unfortunately  for  the 
name  "  syenite,"  both  the  localities  whence  its  name  might 
be  derived  (Mount  Sinai,  and  Syene,  Egypt)  have  this 
variety  of  granite. 

(e)  PROTOGINE-GRANITE,  Jurine  (Haiiy),  "Ai- 

pen-granit "  (Studer). 

A  granite  breaking  with  a  sandy,  crumbly  fracture,  com- 
posed of  abundant  quartz,  scanty  dark  biotite,  abun- 
dant sericite,  white  orthoclase,  microcline  (and  some- 
times an^drthoclase),  with  accessory  small  (M)  grains 
of  garnet,  pyrite,  titanite,  hornblende,  and  sometimes 
large  beryls. 

Silica  66-76. 

This  is  extensively  developed  in  the  Alps  and  is  the  mass 
of  Mont  Blanc.  The  sericite  was  formerly  thought  to  be 
talc  or  chlorite.  The  rock  has  undergone  extensive  altera- 
tion, so  that  in  addition  to  the  change  of  biotite  to  sericite 
the  plagioclase  has  become  saussurite,  and  the  orthoclase 
kaolin  and  sericite.  On  the  peripheries  of  the  granite 
masses  there  is  a  widely  developed  change  of  structure  from 
massive  to  schistoid,  as  will  be  noted  later. 

Here  follow  a  series  of  variations  in  texture  and  structure 
that  effect  all  or  most  ol  the  foregoing  granites  to  a  greater 
-or  less  degree,  and  also  some  variations  in  the  ingredients 
that  are  insufficient  to  cause  the  rock  to  form  a  definite  sub- 
jspecies : 

Miarolite  (Fournet).  This  is  a  cavernous,  drusy  granite, 
rich  in  soda  or  soda-potash  feldspars.  "  Miarolo  "  is  the 


PRIMARY  ROCKS.  133 

Italian  folk-name  for  the  rock.  The  specimen  described 
by  Fournet  came  from  Lyons.  It  is  also  found  in  the 
Vosges ;  the  Mourne  Mountains,  Ireland;  and  in  Italy. 
From  this  structure  Rosenbusch  has  drawn  the  name  miaro- 
litic  for  all  drusy  granites.  The  structure  is  peculiar  to  the 
muscovite  varieties. 

Spherophyric  Granite,  Pudding-granite,  Variolitic  Granite 
(v.  Chrustschoff).  A  granite  containing  concretions  of  a 
concentric-shaly  (rarely  of  a  radial)  structure.  This  is  not 
common  in  granite  ;  but  is  more  frequent  with  varieties  rich 
in  biotite  and  hornblende  than  in  muscovite.  The  con- 
cretions are  composed  of  predominant  mica ;  of  scanty 
quartz  and  mica  (at  Craftsbury,  Vt.) ;  of  concentric  layers  of 
a  compound  alternately  rich  and  poor  in  mica ;  of  a  horn- 
blendic  or  feldspathic  kernel  with  external  growths,  as 
feldspathic  aggregates  of  pegrnatitic  structure,  and  (in 
Siberia  and  Finland)  as  apparently  uniform  bodies.  These 
vary  from  minute  grains  to  masses  eighteen  inches  in  di- 
ameter. The  rock  is  found  in  the  Fichtelgebirge,  France, 
Sardinia,  Sweden,  and  in  the  United  States  in  Colorado, 
Craftsbury,  Vt.,  southern  Rhode  Island  (where  the  concre- 
tions have  the  rare  radial  structure),  and  in  California. 

Schistoid  Granite.  Here  will  be  placed  those  states  found 
on  the  selvages  of  dikes  and  bosses  where,  through  pressure 
during  or  after  cooling,  the  minerals,  especially  mica,  as- 
sumed a  position  parallel  to  the  walls  of  the  country-rock. 
Many  of  these  states  have  been  classed  with  the  gneisses,  as 
in  protogine-gneiss,  but,  even  when  they  are  of  large  extent, 
they  can  be  traced  to  a  central  portion  which  shows  no 
signs  of  foliation.  They  are  also  found  in  shear-zones,  so 
that  we  may  have  schistoid  structures  imposed  on  rocks 
without  their  undergoing  sedimentation.  When  these 
variations  result  in  a  perfect  foliation,  the  rock  must  be 
classed  as  secondary,  but  the  transitional  states  that  are 


134  MANUAL    OF  LITHOLOGY, 

neither  massive  nor  schistose  will  be  styled  "  schistoid,"  as 
above.  Under  this  will  come  the  alternations  of  granite 
and  tourmaline  rock  in  Cornwall,  the  parallel  arrangement 
of  minerals  in  dike-selvages,  etc.  Examples  of  this  are 
found  at  Port  Deposit,  Md. ;  and  abundantly  along  the  shores 
of  Lake  Superior,  in  Europe,  etc. 

PORPHYRIES   OF  THE   GRANITE   GROUP. 

II*.  GRANITE-PORPHYRY  (Kittel). 

A  brownish,  greenish,  sometimes  yellowish,  but  gener- 
ally not  very  dark,  completely  crystalline  (m)  ground- 
mass  of  predominant  feldspar  and  quartz,  carrying 
phenocrysts  of  orthoclase  (gray,  flesh-red,  brick-red), 
mostly  twinned,  yellowish  or  greenish  plagioclase, 
gray  to  dark-colored  grains  of  quartz,  plates  and 
hexagonal  tables  of  brown  mica,  or  rounded  aggre- 
gates of  chlorite  ;  with  accessory  magnetite,  zircon, 
apatite,  pyrite,  infrequent  titanite,  rarely  red  garnet, 
iolite,  or  pinite — the  accessories  generally  (m). 
Silica  61-75  J  GT.  2.6-2.7. 

It  occurs  almost  entirely  in  large  dikes  which  have 
parallel  structures  along  the  selvages,  as  in  other  dike- 
forms,  especially  when  mica  is  present.  In  the  Eureka  dis- 
trict, Nev.,  the  selvages  of  a  granite  dike  are  granite-por- 
phyry. It  is  unknown  in  surface  forms,  and  is  found  abun- 
dantly in  the  Thuringian  Forest,  the  Drusenthal,  Erzge- 
birge,  Bohemia,  Vosges,  France,  Egypt,  China,  and  in  the 
western  United  States  at  Goose  Creek,  Franklin  Buttes, 
Eureka  district,  Nev.,  and  Parkview  Peak,  Col.  It  is 
intermediate  between  granite  and  quartz-porphyry,  which 
it  becomes  by  gaining  a  felsitic  base.  The  groundmass  is 
(m)  wholly  crystalline  with  predominant  feldspar,  which  is 
idiomorphic  with  respect  to  quartz,  and  interlocked  by  it  as 


PRIMARY  ROCKS.  135 

in  granite.  Black  bisilicates  are  rare  in  typical  forms  with 
a  full  quartz  content ;  but  biotite  and  chlorite  appear  as 
quartz  disappears.  Muscovite  is  of  little  importance  ex- 
cept in  the  porphyries  of  kammgranite  (see  p.  130).  The 
quartz  is  sometimes  as  large  as  a  walnut.  Feldspar  varies 
between  tabular  and  prismatic  shapes ;  orthoclase  is  some- 
times three  inches  long  ;  plagioclase  is  usually  oligoclase  or 
oligoclase-andesine,  but  is  seldom  more  basic.  Biotite  is  in 
sharply  denned  hexagonal  tables,  and  alters  to  chlorite. 
Hornblende  is  green  (seldom  brown),  and  chloritizes  and 
epidotizes  readily.  Pyroxene  is  usually  monoclinic  and  green, 
and  usually  serpentinized  or  chloritized— it  also  alters  to 
carbonates.  The  three  black  bisilicates  are  in  nearly  equal 
proportion,  but  the  local  increase  of  each  enables  us  to  dis- 
tinguish varieties.  The  most  common  is  with  biotite,  as 
the  micas  have  the  greatest  affinity  for  acid  minerals. 

(a)  Granitic  Granite-porphyry  (v.  Cotta),  where  the  matrix 
can  be  recognized  as  extremely  fine-crystalline,  but  where 
it  carries   phenocrysts  of  all  the   three  granitic   minerals, 
quartz,  orthoclase,  and  mica.     Common  in  the  Erzgebirge, 
near  Freiberg,  in  the  Thuringian  Forest,  etc. 

(b)  Biotite-granite-porphyry.     Under  this  variety  comes 
the  original  granite-porphyry  noted  by  Kittel  from  Aschaf- 
fenburg. 

1.  Aschaffite  (Giimbel).     A  fine-grained  to  compact  mass, 
rich  in   mica,  and  with  hornblende  and   augite,  carrying 
phenocrysts  of  quartz  and  sporadic  large  feldspars  (single 
and  twinned) ;  but  all  have  their  edges  rounded  by  abrasion 
received  during  eruption,  so  that  sections  are  elliptical.     The 
large  mica  content  makes  this  rock  a  transition  to  the  ker- 
santites,  so  that   it   may  be   complementary   to    an   aplite 

orm  of  granite  by  differentiation  from  a  granitic  magma. 

2.  Alsbachite  (Chelius).     From  the  west  side  of  the  Meli- 
bocus.    Silica  73-75.     It  occurs  in  a  dike  in  granite  ;  brown 


136  MANUAL    OF  LITHOLOGY. 

or  red  ;  with  (M)  quartz,  feldspar,  large  laminae  of  mica,  and 
rose-red  garnets.  The  filling  of  the  same  dike  changes  to 
aplite  when  it  enters  the  gneiss  of  the  east  side  of  the  moun- 
tain. Here  we  have  the  differentiation  of  granite  in  the 
same  dike. 

(c)  Hornblende-granite-porphyry,   where   hornblende   is 
quite  abundant  among  the  other  phenocrysts.     It  occurs  in 
the  Vosges  (where  it  resembles  minette)  and  in  Nevada. 

(d)  Pyroxene-granite-porphyry,  with   abundant  pheno- 
crysts of  pyroxene.     It  occurs  in  Minnesota,  Sweden,  etc. 

Grorudite  (Brogger).  From  Grorud,  near  Christiania. 
A  fine-grained,  greenish  (m)  groundmass  of  orthoclase,  asgi- 
rite,  and  quartz.  A  similar  rock  from  Varingkollen  afforded 
silica  74,5. 

(e)  Chloritic  Granite-porphyry  (v.  Cotta),  Green  Porphyry 
(Naumann),    so-called  "  Syenit-porphyr,"    where   the  black 
bisilicates  have  chloritized,  and  the  rock  assumes  a  green- 
ish color.    The  groundmass  is  fine-  to  micro-crystalline,  and 
brown  to  dark  green,  and  composed  of  flakes  of  chlorite, 
quartz,  and  feldspar,  with  phenocrysts  of  the  same.     It  is 
found  in  the  Erzgebirge,  and  elsewhere  in  Germany. 

II*.  QUARTZ-PORPHYRY,  Elvan  (Cornish  mining 

term),  Quartzophyric  Felsophyre  (Dana). 
A   compact  groundmass   not  resolvable   (M),   carrying 
phenocrysts  of  quartz,  orthoclase,  and  generally  plagi- 
oclase,  with  one  or  more  of  the  black  bisilicates. 
Silica  69-81 ;  Gr.  2.5-2.7. 

It  occurs  principally  in  dikes,  which  have  intersected, 
and  been  extruded  upon  strata  of  varying  ages  from  early 
geological  time  down  to  the  Eocene.  In  one  case  the  dike 
was  30  feet  wide  and  16  miles  long.  These  dikes,  as  usual, 
send  apophyses  into  the  dike-walls,  and  contain  more  vitreous 


PRIMARY  ROCKS.  137 

states  of  the  rock.  It  rarely  occurs  in  intruded  sheets  or 
isolated  plugs.  It  is  found  in  Germany,  Belgium,  Tyrol, 
Transylvania,  Bohemia,  Great  Britain,  France,  Sweden, 
Italy,  Spain,  Sardinia,  Corsica,  Egypt,  Japan,  China,  Brazil,, 
and  in  the  United  States  in  New  England,  Pennsylvania, 
Michigan,  Colorado,  Nevada,  etc.  It  is  the  porphyry  of 
granitite  (biotite-granite).  The  groundmass  fuses  in  thin 
splinters  bp.,  and  is  Vogelsang's  "  granophyre  "  (see  p.  56), 
and  may  be  microgranitic  or  micropegmatitic ;  its  reddish 
color  is  due  to  ferrite  (see  p.  53).  Of  the  phenocrysts,  quartz 
varies  from  minute  grains  to  the  size  of  peas,  either  rounded 
or  in  double  pyramids,  with  grayish  or  dark  smoke-gray 
color  and  vitreo-greasy  luster.  When  (M)  quartz  disap- 
pears, the  rock  becomes  Tschermak's  felsite-porphyry.  (m) 
both  granitic  and  trachytic  structures  are  seen  in  the 
quartz,  as  would  be  the  case  when  it  formed  under  great  or 
small  pressures.  Orthoclase  is  usually  colorless,  yellow- 
ish-white, or  flesh  red  (and  of  lighter  color  than  the  ground- 
mass),  and  its  cleavage  surfaces  have  a  strong  pearly 
luster.  It  occurs  in  tabular  or  prismatic  shapes,  as  in 
granite-porphyry  ;  and  the  large  phenocrysts  commonly 
twin  in  Carlsbad  forms,  less  frequently  in  those  of 
Baveno,  least  in  those  of  Manebach.  Stout  twins  an 
inch  long  are  frequent,  and  with  (M)  inclusions  of  other 
minerals.  A  sanidine-like  habit  in  the  feldspar  causes  a  tra- 
chytic facies  in  the  rock.  The  Washoe  quartz-porphyry 
carries  feldspar  of  so  vitreous  a  habit  that  it  was  misnamed 
dacite  (when  fresh)  and  quartz-propylite  (when  weathered). 
Plagioclase  is  distinguished  from  fresh  orthoclase  by  its 
white  color,  its  softness  and  incipient  kaolinization,  so  that 
striations  are  infrequent.  It  is  usually  oligoclase  or  one  of 
the  albite-oligoclase  series.  Perthitic  structures  are  com- 
mon between  orthoclase  and  plagioclase.  These  min- 
erals (m)  are  usually  like  their  forms  in  granite ;  but 


138  MANUAL    OF  LITHOLOGY. 

orthoclase  in  many  cases  has  the  habit  of  sanidine,  as 
just  mentioned.  Orthoclase  weathers  to  kaolin,  muscovite, 
and  sericite ;  plagioclase  epidotizes.  Microcline  is  not 
as  abundant  as  in  granite.  Biotite  shows  hexagonal  dark- 
green  or  brown  tables ;  muscovite  is  seldom  alone  in 
the  groundmass,  but  sometimes  is  one-third  of  an  inch  in 
size.  Only  few  varieties  carry  hornblende  in  abundance  ;  it 
is  sometimes  in  prisms  visible  with  a  lens,  as  in  the  Truckee 
rock.  Pyroxene  is  as  in  granite.  As  accessory  (M)  minerals 
are  cordierite  (iolite),  garnet  (Twin  Mountains.,  N.  H.), 
tourmaline,  topaz,  fluorite,  orthite  (Colorado),  and  zeolites. 
Some  varieties  have  abundant  concretions,  as  in  granite. 
The  structure  of  quartz-porphyry  varies  from  massive  to 
amygdaloidal,  cavernous,  fissured,  and  cracked.  The  first 
two  are  filled  with  calcite,  quartz,  chalcedony,  hornstone, 
opal,  jasper,  and  amethyst  ;  the  others  only  with  crystals. 
Occasionally  a  vesicular  structure  with  parallel  arrange- 
ment is  met  with  (cavities  sometimes  two  inches  long).  In 
rare  cases  small  slaggy  particles  appear  in  the  dense  ground- 
mass,  which  may  be  pyroclasts  of  portions  of  the  first  erup- 
tion that  cooled  against  the  dike-walls,  and  have  been  partly 
re-fused  in  the  mass.  In  addition  to  concretions  there  are 
also  compact,  radial,  or  concentric-shelly  spheroids,  which 
are  sometimes  like  rhyolitic  lithophysas  (South  Mountain, 
Pa.  and  Md.).  (M)  fluidal  structures  are  common,  especially 
along  selvages.  Quartz-porphyry  weathers  to  clay-porphyry, 
clay  stone,  and  kaolin.  It  occurs  with  irregular  fissures;  some- 
times with  columnar  and  tabular  jointing,  as  in  basic  dike- 
rocks.  The  great  proportion  of  accessory  minerals  is  due 
to  infiltration  into  the  cracks,  nests,  etc.  Dendritic  mark- 
ings are  common,  as  well  as  stainings  from  ferruginous 
solutions,  as  the  mass  weathers.  Spheroidal  weathering  is 
rare. 

a.  Typical  Quartz-porphyry.     A  compact   matrix  with 
phenocrysts  of  quartz,  feldspar,  and  sometimes  mica   and 


PRIMARY  ROCKS.  139 

hornblende,  rarely  pyroxene.     According  to  the  texture  of 
the  matrix  it  can  be  divided  into : 

1.  Hormtone- porphyry,  Elvan,  with    a   cryptocrystalline 
groundmass  that  breaks  with  a  splintery  fracture  like  chert, 
and  has  a  faint  glimmer  or  waxy  luster  on  a  freshly  broken 
surface.     It  will  strike  fire  with  steel,  but  can  be  told  from 
.hornstone  by  its  fusibility. 

2.  Felstone-porphyry,  when  the  compact  mass  is   not  so 
hard,  and  has  a  smoother  fracture. 

j.  Clay  stone-porphyry,  Argillophyre,  when  there  is  a 
rough,  almost  earthy  groundmass,  soft  enough  to  be  cut 
with  a  knife.  This  is  the  state  of  (i)  and  (2)  after  weather- 
ing. This  last  occurs  extensively  at  Leadville,  Col.,  under 
the  name  of  white-porphyry.  It  joints  readily  into  blocks, 
whose  faces  are  covered  with  dendritic  markings. 

4.  Pyritiferous  Porphyry.  A  decomposed  hornblende- 
biotite  variety,  with  those  minerals  replaced  by  pseudo- 
morphs  of  pyrite.  From  Leadville,  Col.,  where  it  has  been 
formed  from  quartz-porphyry  by  the  action  of  thermal 
waters  charged  with  HaS.  The  hornblende-biotite  variety 
is  found  in  a  fresh  state  at  depths  in  the  mines,  but  near  the 
outcrops  the  hornblende  has  disappeared,  and  is  represented 
by  pyrite,  as  above  stated,  while  the  biotite  has  been 
-altered  to  chlorite  and  pyrite.  The  quartz-porphyry  of 
Freiberg  has  a  small  quartz  content  and  carries  pyrite. 

(a)  Beresite  (G.  Rose).  A  dike-rock  from  Beresowsk 
in  the  Urals,  and  elsewhere  which  is  much  decomposed. 
It  shows  kaolinized  orthoclase  and  plagioclase,  pyrite, 
and  not  much  quartz  nor  mica,  and  occurs  with  auriferous 
veins.  It  was  once  thought  to  be  a  dike-form  of  musco- 
vite-granite,  but  Helmhacker  places  it  under  quartz-por- 
phyry. 

j".  Slaty  Porphyry,  Band  Porphyry,  Striped  Porphyry. 
The  result  of  flow,  and  composed  of  layers  of  different  color, 
composition,  or  texture.  These  are  usually  parallel  to 


I4O  MANUAL   OF  LITHOLOGY. 

the  selvages  of  the  dike ;  are  often  bent  and  twisted,  and 
(m)  are  found  to  be  of  alternately  coarse-  and  fine-crystalline 
texture.  In  many  cases  the  parallel  arrangement  of  color  is 
accompanied  by  a  decided  schistose  structure,  so  that  the 
rock  splits  more  readily  with  than  against  the  layers.  An- 
other variety  of  slaty  porphyry  is  due  to  orogenic  forces. 
Examples  of  the  first  are  found  near  Freiberg,  in  the 
Thuringian  Forest,  etc.;  of  the  second,  in  Switzerland, 
France,  Nassau,  etc. 

6.  Millstone-porphyry,    Drusy    Porphyry,    Porous    Por- 
phyry.    A  quartz-porphyry  filled  with  irregular  druses  and 
geodes,  which  are  usually  the  result  of  weathering,  are  not 
vesicular,   and    are    lined    with    thin   layers   of  hornstone,, 
chalcedony,  amethyst,  calcite,  fluorite,  specular  iron,  etc.    It 
is  quarried  for  millstones  (whence  the  name),  and  is  found 
in    the    Erzgebirge,     Thuringian    Forest,     Fichtelgebirge, 
Odenwald,  Schwarzwald,  etc. 

7.  Vesicular  Porphyry.     A  rare  variety,  with  numbers  of 
steam  blow-holes  (sometimes  two  inches  long),  drawn  out 
by  flow  and  arranged  in  parallel  structure,  or  with  small 
vesicular  pyroclasts  enclosed  in  a  dense  groundmass.     The 
former  is  found  at  Rochlitz,  Saxony,    and   Friedrichroda, 
the  latter  in  the  Falkenstein.     In  some  cases  these  are  filled 
with  quartz  and  specular  iron  to  form  amygdaloidal porphyry ~ 

8.  Pyromeride  (Haiiy),  Ball  Porphyry.   A  variety  abound- 
ing in  spheroids  in  addition  to  the  usual  crystals.     It  is 
found  in  the  Thuringian  Forest,  Harz,  Corsica,  Eiba,  Sar- 
dinia, Jersey,   and   in   the   western   United   States   and   in 
Pennsylvania.      The  balls  are  compact,  radial-fibrous,  and 
shelly.     Some  are  like  lithophysae  in  rhyolite,  and  the  rock 
may  have  been  derived  from  that  extrusive  by  devitrifica- 
tion.    The  cavities  in  the  balls  are  filled  with  hornstone, 
agate,  etc.     It  is  found  with  both  microgranitic  and  micro- 
pegmatitic  groundmasses. 


PRIMARY  ROCKS.  141 

(b)  Samdme-quartz-porpriyry.      A   variety   containing 
sanidine  from  Baden-Baden,  southern  Tyrol,  and  Zwick- 
au, Saxony.     These  are  geologically  late  varieties,  and, 
probably  on   that  account,  near  the  tops  of   the  dikes. 
The   feldspar   is   fresh   sanidine,    with   high   luster,   well 
fissured,  and  easily  fractured. 

(c)  Hornblende-quartz-porphyry.     A  variety  with  large 
(^  inch)  hornblende  columnar  phenocrysts,  in  a  greenish- 
gray   to   grayish   groundmass.      It    is    found    at   Mount 
Sinai,  the   Pyrenees,  Sardinia,  France,  Germany,  Corea, 
Scotland,  and  Nevada. 

(d)  Pyroxene-quartz-porphyry.    A  variety  with  pyrox- 
ene  phenocrysts  that   can  be  distinguished  with  a  lens 
(sometimes  -fa  inch  long).     It  is  usually  monoclinic  and 
serpentinized.     The  rock  is  found  in  Siberia,  Alsace,  Eng- 
land, Egypt,  and  in  New  Hampshire  at  Waterville. 

lie.  FELSITE-PORPHYRY  (Tschermak). 
A  quartz-porphyry  where  the  quartz   is   in  (m)  pheno- 
crysts,  and   the   only   (M)  phenocrysts   of    feldspar 
appear. 

As  quartz  is  in  phenocrysts,  though  (m),  the  rock  is  a 
true  quartz-porphyry.  The  groundmass  is  colored  red 
or  brown  by  ferrite,  and  shows  phenocrysts  of  feldspars, 
.hornblende,  and  specular  iron.  It  is  found  in  Sweden, 
Nassau,  China,  etc. 

Here  belong  the  states  of  Giimbel's  keratophyre,  which 
are  quartzose  and  have  a  compact  groundmass  (see  "  Kerato- 
phyre," p.  155).  Such  a  soda-orthoclase-quartz-porphyry  is 
found  at  Pigeon  Point,  Minn.,  as  a  (m)  fine-grained  ground- 
mass,  of  dark-red  or  purple  color,  carrying  phenocrysts  of 
•greenish-white  and  brick-red  feldspars.  It  is  said  to  form 
the  contact  product  of  gabbro  on  slate.  If  so,  it  is  an  in- 
stance of  a  transition  between  a  sediment  and  an  eruptive. 


142  MANUAL   OF  LITHOLOG  Y. 

GRANITIC   FELSOPHYRES. 

lid.  FELSITE  (Gerhard),  Eurite  (Daubuisson),  Pe- 

trosilex  (Brongniart). 

A  compact  rock  as  hard  as  feldspar ;  yellowish,  reddish, 
gray,  greenish,  bluish ;  weathering  white,  with  dull, 
smooth,  conchoidal,  or  fissile  fracture.  It  has  the  same 
(m)  composition  as  the  groundmass  of  quartz-por- 
phyry, and  like  it  fuses  in  thin  splinters. 
Silica  71-81  ;  Gr.  2.5-2.7. 

It  occurs  in  masses  1500  feet  thick,  and  in  dikes,  abun- 
dantly in  Great  Britain  and  in  Saxony,  elsewhere  less  abun- 
dantly as  a  state  of  quartz-porphyry.  It  has  a  massive- 
jointed  structure,  but  is  not  so  much  fissured  as  quartz- 
porphyry.  Devitrification  has  been  claimed  as  the  agent 
which  has  altered  this  from  an  extruded  glass.  In  many  cases 
it  holds  spherules,  which  Rutley  claims  to  indicate  that  the 
rock  in  question  is  a  devitrified  perlite.  It  shows  fluxion 
and  parallel  structures,  and  in  this  respect  resembles  halle- 
flinta,  which  v.  Cotta  classed  here,  and  which  has  just  been 
shown  to  be  a  devitrified  rhyolite.  Parallel  structures  are 
shown  on  a  grand  scale  in  Great  Britain,  where  high  moun- 
tains are  formed  of  this  rock. 

GRANITE   GLASS. 

Ilia.    PITCHSTONE-  PORPHYRY,    Vitrophyre 

(Vogelsang). 

A  compact  glass,  with  considerable  water,  of  greasy, 
resinous  luster,  conchoidal  fracture,  translucent  on 
thin  edges,  with  the  hardness  of  feldspar  ;  colored 
olive-green,  blackish  green,  yellowish  brown,  brown- 
ish red,  and  black;  exhibiting  (M)  phenocrysts  of 
vitreous  feldspar,  laminae  of  mica  (biotite),  grains  of 
quartz,  and  reddish  spheroids. 


PRIMARY  ROCKS.  143 

PITCHSTONE,  Retinite. 
A    similar    glass    entirely   free   from    phenocrysts   and 
spherules. 

Silica  63-76;  Gr.  2.25-2.4;  water  5-8$. 

This  occurs  in  beds  or   sheets   2000  feet  thick,  also  in 
bosses  and  dikes,  and  usually  associated  with  quartz-por- 
phyry.    It  is  especially  found  in  the  vicinity  of  Meissen,  the 
Fichtelgebirge,  Tyrol,  Italy,  Arran,  Scotland;   and  in  the 
United  States  at  Isle  Royal,  Lake  Superior,  and  in  Colorado. 
.The  groundmass  (m)  is  seldom  free  from  phenocrysts,  which 
are  of  the  minerals  noted  under  quartz-porphyry.     There 
are  two  types  of  the  rock — trachytic  and  felsitic — associated 
with  the  rocks  of  the  name.     They  are  alike  at  sight  and 
under  chemical  analysis,  and  only  the  microscope  can  distin- 
guish between  them.     Orthoclase  is  fresh  and  like  sariidine  ; 
plagioclaseisoligoclase-labradorite:  quartz  occurs  in  double 
pyramids.     In  the  groundmass  are  (m)  augite,  hornblende, 
apatite,  zircon,  magnetite,  tridymite,  and  hyalite,  but  rarely 
and  scantily.     The  regular  spheroids  vary  from  (m)  propor- 
tions to  six  inches,  and  the  irregular  ones  may  be  two  feet. 
The  smaller  ones  are  felsitic  (sometimes  like  sanidine),  with 
starry   internal   cracks  lined   with   (m)  quartz,  chalcedony, 
agate,  etc.   The  larger  ones  are  irregular,  sometimes  angular 
and  with  re-entering  angles,  sometimes  roughly  rounded  as 
by  abrasion.    These  latter  are  pyroclasts  of  quartz-porphyry, 
and  even  spherulitic  pitchstone  rent  from  older  masses,  and 
somewhat  metamorphosed,  as   their   peripheries  are  more 
dense  than  their  interiors.     They  contain  spherules  of  differ, 
ent  character  from  those  of  the  enclosing  mass  (near  Meissen), 
and  are  older  than  it,  as  their  nodules  are  rusty  and  weath- 
ered.    The    Planitz    (Saxony)    pitchstones   contain    mineral 
charcoal  pyroclasts  from  coal  deposits  through  which  they 
have  broken.     Those  near  Zwickau  and  Wechselburg  show 
devitrification,  as  the  selvages  are  quartz-porphyry  (with  a 
crystalline  groundmass  in  the  latter  instance). 


144  MANUAL    OF  LITHOLOGY. 

Argillaceous  Pitchstone,  Pitchstone-felsite  (Naumann),  "  Ar- 
gilorelinite."  From  near  Meissen,  somewhat  weathered, 
wax-yellow  or  olive-green,  conchoidal  fracture,  and  greasy 
luster.  Silica  79.85. 

INTERMEDIATE    DIVISION— AMPHIBOLE   ROCKS. 

These  are  intermediate  in  two  ways — through  the  alkali 
minerals  (orthoclases  and  feldspathoids),  and  through  the 
lime-soda  minerals  (plagioclases),  as  follows : 

I.  ALKALI  SECTION: 

(a)  Groups  3  and  4.   Alkali  feldspar,   plagioclase,  feldspathoids, 
quartz,  mica,  pyroxene,  magnetite,  olivine. 
Extrusive,  Trachyte  ;  Intrusive,  Syenite. 

(&)    Groups  5  and  6.  Alkali  feldspar,  feldspathoids,  plagioclase, 
quartz,  mica,  pyroxene,  magnetite,  olivine. 

Extrusive,  Phonolite;  Intrusive,  Elaeolite-syenite. 

II.  ALKALI-LIME-SODA  SECTION: 

(a)  Group  7.  Alkali  feldspar,  mica,  quartz,  plagioclase,  pyroxene, 
magnetite,  feldspathoids,  olivine. 

Extrusive,  none ;  Intrusives,  Syenitic  Mica-traps. 

(b)  Groups  8  and   9.   Plagioclase,  mica,  quartz,  pyroxene,  alkali 
feldspar,  magnetite,  olivine,  feldspathoids. 

Extrusive,  none;  Intrusives:   Group  8,  Dioritic  Mica-traps ; 
Group  9,  Porphyrite  and  Mica-porphyrite. 

III.  LIME-SODA  SECTION: 

(a)  Groups  10  and  n.  Plagioclase,  mica,  quartz,  pyroxene,  mag- 
netite, alkali  feldspar,  olivine,  feldspathoids. 

Extrusive,  Dacite ;  Intrusive,  Quartz-diorite. 
(K)  Groups  12  and  13.  Plagioclase,  pyroxene,  mica,  alkali  feldspar, 
magnetite,  olivine,  feldspathoids,  quartz. 

Extrusive,  Andesite  ;  Intrusive,  Diorite. 

(c}  Groups  14  and  15.  Plagioclase,  pyroxene,  magnetite,  olivine, 
mica,  feldspathoids,  alkali  feldspar,  quartz. 
Extrusive,  Pyroxene-andesite  ;  Intrusive,  Pyroxene-diorite. 


PRIMARY  ROCKS.  145 

GROUP  3.     TRACHYTE. 
la.   TRACHYTE-SYENITE  EXTRUSIVES. 
(Necessary  minerals  :  Amphibole  and  an  alkali  feldspar.) 

TRACHYTE  (Haiiy). 

A  rough,  porous,  (M)  microcrystalline  or  aphanitic 
groundmass  carrying  (m)  a  small  proportion  of  glass 
base  with  a  felt  of  minute  crystals  of  sanidine  (and  gen- 
erally plagioclase),  with  small  amounts  of  the  black 
bisilicates,  magnetite,  and  titanite,  and  showing  large 
(M)  phenocrysts  of  sanidine,  plagioclase,  and  (in  small 
proportions)  hornblende,  augite,  and  magnesia  mica. 
Quartz,  nepheline,  and  leucite  are  absent,  and  olivine 
generally  so. 

Silica  58-67;  Gr.  2.6;  H.  5-6. 

Trachyte  occurs  in  dome-shaped  masses,  generally  in 
lava-streams,  infrequently  in  dikes,  also  in  tuffs.  It  is  ex- 
tensively developed  in  western  Germany,  Hungary,  France, 
Spain,  Italy,  Asia  Minor,  East  Indies,  Azores,  South  Africa, 
New  Zealand.  It  forms  the  greatly  extended  and  most 
acid  of  recent  lavas.  The  groundmass  differs  from  that  of 
rhyolite  in  the  almost  entire  absence  of  a  vitreous  portion,  and 
fewer  developments  of  fluxion  structure.  Zirkel  states  that 
the  roughness  of  the  groundmass  is  due  to  (a)  the  fact  that 
the  crystals  of  the  mass  are  not  intergrown,  as  in  granite,  but 
touch  at  but  few  points,  so  as  to  leave  interstices,  and 
(b)  that  there  are  many  round  or  egg-shaped  gas-pores 
which  form  trachyte-pumice  when  they  comprise  the  greater 
part  of  the  mass.  Trachyte  is  generally  considered  a  por- 
phyritic  rock.  The  usual,  colors  are  brownish,  yellowish 
white,  reddish,  gray,  and  (rarely)  bluish.  The  name  refers 


146  MANUAL  OF  LITHOLOGY. 

to  the  rough  feeling  of  the  groundmass  (from  the  Greek  for 
rough)  when  the  fingers  are  rubbed  over  the  fractured 
surface  of  a  fresh  specimen.  The  pores  above  mentioned 
cause  the  rock  to  fracture  irregularly  and  unevenly.  The 
luster  differs  from  that  of  rhyolite  in  being  dull,  and,  at  best, 
clayey  and  semivitreous.  The  feldspar  seems  to  be  the 
prevailing  mineral.  Of  the  phenocrysts,  sanidine  appears 
in  tabular  crystals,  crystalline  grains,  and  fragments.  Twin- 
ning occurs  in  Carlsbad  and  Baveno  types.  Anorthoclase 
is  reported  in  an  acmite-trachyte  from  South  Africa,  and 
microcline  in  an  andesitic  variety  from  the  Azores.  Plagio- 
clase  occurs,  striated  and  white,  with  high  luster,  but  in 
much  smaller  individuals  than  does  sanidine/  The  old  divi- 
sions into  sanidine  and  oligoclase  trachytes  were  based  on 
the  (M)  examination  of  the  phenocrysts,  but  they  cannot 
hold,  as  plagioclase  is  generally  present  in  all  trachytes, 
and  especially  in  the  groundmass,  and  the  divisions  are 
now  made  by  many  authorities  on  other  grounds.  The 
plagioclase  is  usually  oligoclase  ;  but  albite,  andesite,  and 
labradorite  occur  in  a  few  specimens.  Of  the  black  bi- 
silicates  (hornblende,  augite,  and  biotite),  the  greater  pro- 
portion occurs  as  phenocrysts,  and  not  in  the  groundmass. 
They  form  large  individuals  sparsely  scattered  through  the 
mass.  Augite  seems  to  be  the  only  one  that  appears  alone, 
or  in  company  with  either  of  the  others.  Hornblende  occurs 
in  large,  lustrous,  black,  stout  prisms,  long  needles,  or  irregu- 
lar grains.  The  prisms  have  the  habit  of  basaltic  hornblende. 
In  the  groundmass  arfvedsonite  and  aegirite  appear  (;«)„ 
Hornblende  is  altered  to  chlorite  and  epidote  in  some  tra- 
chytes. Monoclinic  augite  is  seldom  (M)  (as  in  the  Drachen- 
fels  variety).  Acmite  is  occasionally  found.  Rhombic 
pyroxene  (hypersthene)  is  rarely  (M).  Magnesia-mica  in 
black  folia  is  common  in  many  trachytes  (M).  It  is  gener- 
ally biotite  and  in  hexagonal  leaves.  It  is  usually  absent 


PRIMARY  ROCKS.      •-  1 47 

from  the  groundmass,  which  can  thus  be  distinguished  from 
that  of  minette,  when  the  trachyte  carries  a  large  proportion 
of  the  mineral.  Magnetite  (m)  is  more  abundant  than  in 
rhyolite,  and  can  be  gathered  from  the  powdered  rock  with 
the  magnet.  Epidote  and  titanite  occur  as  (M)  accessories. 
Olivine  is  generally  absent;  quartz,  nepheline,  and  leucite 
always  so ;  hauyne  is  present  in  rare  cases  ;  apatite  and  zir- 
con usually  present,  as  in  all  rocks,  in  small  amounts,  but  (m). 

I.  Typical  Trachyte  (of  Rosenbusch).     A  compound  of 
feldspar  with  phenocrysts  of  either  or  both  of  the  minerals 
hornblende   and   biotite,   while   augite   is   confined   to   the 
groundmass.     Under  this  are  distinguished  : 

1.  Biotite-trachyte. 

2.  Biotite-hornblende-trachyte. 

3.  Hornblende-trachyte. 

Under  the  second  comes  the  so-called  "  oligoclase- 
trachyte,"  or  domite,  from  the  Siebengebirge  and  the  Puy 
de  Dome  (whence  the  name).  It  is  a  dark-colored  com- 
pound of  oligoclase,  hornblende,  and  biotite,  with  (m)  augite. 
Silica  62-68  ;  Gr.  2.6-2.8.  It  is  reddish,  soft,  and  sandy. 

Typical  trachytes  occur  in  Germany,  Hungary,  France, 
Bohemia,  Italy. 

II.  Augite-trachyte  (of  Rosenbusch).     A  compound  of 
feldspar  with   phenocrysts  of  monoclinic  pyroxene,  while 
mica  and  hornblende  are  absent,  or  play  a  very  unimportant 
part.     This  variety  is  important  in  Italy. 

i.  Acmite-trachyte  (Miigge).  First  noted  from  the  Trans- 
vaal, also  from  Crazy  Mountains,  Mont.  In  the  latter 
regions  it  is  in  sheets,  dikes,  and  laccoliths.  The  rock  is 
composed  of  a  groundmass  of  lath-shaped  feldspars  and 
acicular  segirites  and  acmites,  with  colorless  interstitial 
matter,  and  carrying  phenocrysts  of  anorthoclase,  sodalite, 
and  augite.  The  interstitial  matter  is  composed  (?)  of 
nepheline  and  analcite.  Silica  62.17. 


I48  MANUAL    OF  LITHOLOGY. 

III.  Phonolitic  Trachyte  (of  Zirkel).    A  compound  of 
feldspar  (sanidine,  anorthoclase,  oligoclase),  augite,  sparse 
biotite  and    hornblende,   (in)   segirite   and  acmite,  and   (in 
druses)  sodalite  and  sometimes  nepheline.     Nepheline  does 
not  occur  as  a  typical  ingredient  of  the  mixture.     These 
trachytes  are  found  at  Monte  di  Cuma,  Ischia,  San  Miguel 
and  Terceira  of  the  Azores,  and  Massai  Land,  South  Africa. 
Its  greenish  groundmass  is  sometimes  schistose. 

IV.  Andesitic  Trachyte  (of  Miigge).  A  dark  to  blackish 
gray  compound  of  feldspar  (mostly  triclinic),  with  a  great 
proportion  of  (m)  black  bisilicates  and  ores  in  the  ground- 
mass,  which  carries  a  distinct  amount  of  dark-colored  glass. 
Among   the   phenocrysts    appear    feldspars   of   good   size, 
augite,  biotite,  and  sometimes  olivine.    Hornblende  is  rarely 
present.    The  microstructure  is  trachytic,  and  thus  separates 
the   rock   from   the   andesites.      The   rock   epidotizes   and 
uralitizes.     It  occurs  at  Schemnitz,  the  Arso  lava  of  Ischia, 
the  Azores,  and  Mont  Dore  in  Auvergne. 

V.  Hypersthene-trachyte  (J.  F.  Williams).      This  is  a 
rock  first  studied  at  Monte  Amiata,  with  63-67  per  cent  of 
silica.      It   is   andesitic,   but   of  grayish  or  reddish  color, 
with  sanidine,  hypersthene,  and  a  high   acidity.     Bronzite- 
trachyte  is  reported  from  Japan. 

To  the  trachytes  are   annexed   certain   rocks   that  are 
found  geologically  connected  with  them,  as  : 

VI.  Laacher  Trachyte  (v.  Dechen).     In  the  tuffs  about 
the  lake  of  Laach  are  round  masses  of  a  sanidine-trachyte  not 
found  in  place  in  the  neighborhood.     It  is  partly  compact, 
partly  porous,  light-  to  dark-gray  groundmass,  with  pheno- 
crysts of  white  sanidine,  and  partly  intergrown  with  them 
and  partly  in  druses   are   hauyne  (or  nosean),  hornblende, 
augite,  mica,  olivine,  plagioclase,  and  titanite.     The  ground- 
mass  often  carries  an  abundant  porous  glass.     In  the  Azores 


PRIMARY  ROCKS.  149 

is  a  somewhat  similar  rock.  This  is  also  called  haiiyne- 
trachyte. 

VII.  Sanidinite  (Zirkel),  Sanidine  Bombs.  These  occur  at 
the  same  place,  and  are  composed  of  a  soda-sanidine,  haQyne 
(or  nosean),  augite,  hornblende,  biotite,  plagioclase,  scapolite, 
garnet,  nepheline,  olivine,  hypersthene,  calcite,  apatite,  and 
magnetite.  There  is  neither  quartz  nor  leucite.  It  occurs 
also  in  the  Azores. 

The  trachytes  occur  generally  compact,  porous,  and  por- 
phyritic ;  sometimes  the  pores  become  so  numerous  as  to 
form  scoriaceous  states  on  the  surface  of  lava-flows,  but  the 
vesicles  are  never  filled,  and  the  rock  is  never  amygdaloidal. 
With  the  entrance  of  nepheline  the  rock  passes  into  the 
phonolites ;  with  the  addition  of  a  glassy  groundmass  and 
the  absence  of  alkali  feldspars,  to  the  andesites  ;  and  with  the 
entrance  of  free  quartz,  to  the  rhyolites.  The  products  of 
contact  metamorphism  are  similar  to  basalt. 

(For  "  Trachyte  Glass  "  see  p.  in,  where  it  is  described 
with  rhyolite  glass,  owing  to  the  similarity  between  them.) 

GROUP  4.     SYENITE. 

Ib.   TRACHYTE-SYENITE  INTRUSIVES. 
(Necessary  minerals:  An  alkali  feldspar  and  amphibole.) 

SYENITE  (G.  Rose). 

A  granitoid  compound  of  an  alkali  feldspar  and   horn- 
blende (with  mica,  pyroxene,  and  without  quartz). 
Silica  55-63  ;  Gr.  2.7-2.9. 

All  of  the  varieties  of  this  group  contain  hornblende,  but 
some  have  the  other  black  bisilicates  predominant,  or  as 
prominent  as  hornblende,  so  that  varieties  are  formed  by 
the  variation  of  minerals.  There  is  also  the  same  variation 
in  texture  due  to  rates  of  cooling  as  in  granite,  so  that  the 
following  divisions  are  generally  recognized  : 


ISO  MANUAL    OF  LITHOLOGY. 

I.  Hornblende-syenite,  or  typical  syenite. 

II.  Mica-syenite. 

III.  Pyroxene-syenite. 

IV.  Syenite-porphyry.  . 
V.  Syenite-aphanite. 

These  are  quartzless  granites.  This  statement  must  not 
be  taken  as  preventing  the  admission  of  a  small  amount  of 
that  mineral  to  form  quartzose  varieties,  but  a  large  amount 
would  form  quartz-poor  granites.  V.  Cotta  states  that  near 
Dresden  a  transition  from  syenite  to  granite  can  be  traced 
in  the  same  mass.  As  augite  is  a  usual  component  of 
nepheline  mixtures,  the  augite-syenites  are  more  nearly 
connected  with  the  elseolite-syenites  than  the  other  mem- 
bers of  the  group.  The  more  basic  the  rock  the  more 
plagioclase  is  found  accompanying,  and  replacing,  ortho- 
clase.  Syenites  occur  in  the  same  forms  as  does  granite, 
but  in  smaller  bosses  and  fewer  dikes.  They  joint  less 
readily  than  granite,  and  do  not  weather  spheroidally  as 
readily.  They  differ  from  the  diorites  in  their  feldspar.  A 
iine-grained  syenite  is  sometimes  confused  (M)  with  diorite, 
but  it  can  be  distinguished  by  its  being  red  or  gray,  while 
diorite  is  dark  or  green.  Diorite  is  usually  more  fine- 
grained than  syenite ;  oligoclase  weathers  faster  than  the 
hornblende,  so  that  the  latter  is  prominent  on  a  weathered 
surface,  but  the  rock  remains  solid;  orthoclase  and  horn- 
blende weather  more  nearly  together  in  syenite,  so  that  the 
rock  falls  into  a  rusty  sand.  Diorite  carries  more  pyrite, 
syenite  more  titanite.  When  other  signs  fail,  the  fusibility 
of  the  feldspars  usually  settles  the  question. 

"  Syenite"  is  a  misnomer,  as  the  original  syenites  did 
mot  come  from  Syene,  Egypt,  and  Rozifcre's  Sinaite  would 
be  no  nearer  correct,  as  the  rocks  in  both  localities  are 
hornblende-granite. 


PRIMARY  ROCKS.  !$! 

I.  HORNBLENDE-syenite. 

A  granitoid  compound  of  an  alkali  feldspar  and  primary 
hornblende,  with  plagioclase,  occasionally  biotite  and 
quartz,  and  usually  magnetite,  titanite,  and  apatite. 

It  is  found  in  Saxony,  the  Thuringian  Forest,  Great 
Britain,  Norway,  Sweden,  Bulgaria,  Russia,  Greenland,  New 
.Zealand,  Nevada,  Arkansas,  Massachusetts,  etc.  Orthoclase 
is  usually  flesh-red,  yellowish  red  with  bluish  schiller,  some- 
times white;  common  in  Carlsbad  twins,  rare  in  Baveno. 
Microcline  is  now  and  then  present.  Both  alter  as  in  granite. 
The  plagioclase  belongs  to  the  soda  end  of  the  series.  Horn- 
blende occurs  in  stout  prisms,  dark-green,  grayish  black  to 
black  (greenish  by  transmitted  light).  Biotite  occurs  in 
brown  (sometimes  green)  irregular  folia,  and  replaces  the 
hornblende,  not  the  feldspar.  It  is  the  oldest  generation 
•of  the  necessary  minerals.  Quartz  occurs  sparingly,  and 
occasionally  forms  a  micropegmatitic  texture.  It  is  usually 
(in).  Apatite  occurs  more  abundantly  as  the  mixture  gro\vs 
basic.  Concretions  of  the  black  bisilicates  with  scanty 
plagioclase  are  common.  The  texture  is  medium  to  coarse 
granitoid,  and  frequently  porphyritic  from  large  feldspar 
phenocrysts  in  some  dike-forms,  which  are  usually  of  ortho- 
clase  (sometimes  three  inches  long),  while  plagioclase  is  absent 
as  phenocrysts.  In  some  localities  there  is  a  parallel  arrange- 
ment of  alternate  feldspathic  and  hornblendic  mixtures.  As 
accessories  occur  titanite,  zircon,  garnet,  orthite — never 
tourmaline ;  as  secondary  products  hornblende  epidotizes, 
while  feldspar  remains  fresh  to  form  epidote-syemte. 

(a)  Nordmarkite  (Brogger).  A  quartzose  syenite  of  flesh- 
red  color,  medium  grain,  minute  drusy  structure,  composed 
of  feldspar  (orthoclase,  microperthite,  and  acid  oligoclase) 
and  quartz,  with  biotite,  hornblende  (arfvedsonite  or 
glaucophane),  light-green  pyroxene,  sparse  asgirite,  titanite, 
zircon,  apatite,  and  iron  ores.  Silica  60-64. 


I52  MANUAL   OF  LITHOLOGY. 

II.  MICA-syenite,  Biotite-syenite. 

A  rare  variety  with  predominant  mica.     It  is  found  in 
Austria,  Norway,  Italy,  Greenland,  Black  Forest,  etc. 
Silica  51. 

(a)  Durbachite   (Sauer).       A    biotite-syenite   with    large 
phenocrysts  of  orthoclase  over  £  inch  long. 

(b)  Augite-bearing  Mica-syenite.     In  Norway,  as  a  transi- 
tion between  the  mica-  and  augite-syenites,  carrying  anortho- 
clase,  cryptoperthite,  oligoclase,  hornblende,  lepidomelane 
in  tables    nearly  half  an  inch  square,  and  augite.      Silica 
55.18. 

III.  PYROXENE-syenite. 

A  syenite  with  predominant  pyroxene.  The  feldspar  is 
orthoclase  (also  anorthoclase  and  microperthite)  and 
a  soda-rich  plagioclase.  The  pyroxene  may  be  a 
titaniferous  diallage  or  diopside,  augite,  hypersthene, 
or  uralite.  Mica  is  usually  biotite,  sometimes  lepi- 
domelane ;  elaeolite  is  seldom  absent  in  some  varieties. 
Hornblende  is  brown.  Olivine  is  usually  present, 
and  quartz  and  plagioclase  absent.  In  color  it  is 
grayish,  greenish,  brick-red,  blackish  green,  and  violet- 
red  when  weathered.  It  resembles  gabbro  in  some 
varieties. 

Silica  55-59. 

This  combination  is  not  a  common  one,  though  it  is  of 
importance  in  Norway,  Italy,  and  less  prominent  elsewhere. 

(a)  Orthoclase -monzonite.      A    compound   of   orthoclase, 
plagioclase,  hornblende,  and  augite,  with  an  abundance  of 
the  ores.     At  Monzoni,  Italy,  and  in  Silesia. 

(b)  Laurvikite  (Brogger).     From  southern  Norway,  with 
56.8-58.8  silica.     A  grayish  gabbro-like  rock  composed  of 
brown  hornblende,  the  soda-orthoclases,  titaniferous  pyrox- 
ene, biotite,  and  some  nepheline  and  olivine. 


PRIMARY  ROCKS.  1 53 

(c)  Akerite  (Brogger).     A  quartzose  variety  of  the  above 
and   at   the   same   place,  carrying   orthoclase,  plagioclase, 
quartz,  hornblende,  pyroxene,  brown  biotite ;  no  nepheline, 
sodalite,  nor  olivine.    It  is  in  a  laccolith ;  medium-  to  coarse- 
grained and  granitic  ;   gray  to  red.     The  variety  from  New 
Hampshire  described  by  Hawes  is  like  this. 

(d)  Hypersthene-syemte.     Zirkel  places  here  the  "  norite" 
of  G.  H.  Williams,  from   Cortlandt,  N.  Y.,  as  it  contains 
orthoclase. 

(e)  Uratite-syemte  (v.  Jeremejew).     A  uralitized  augite- 
syenite  from  the  Urals. 

PORPHYRIES    OF  THE   SYENITE  GROUP. 

IV.  SYENITE-PORPHYRY  (v.  Richthofen). 
This  subgroup  includes  the  quartzless  orthophyric  felso- 
phyres  that  exhibit  phenocrysts  of  one  or  more  of  the  black 
bisilicates  to  form  a  series  which  has  the  same  relation  to 
syenite  that  quartz-porphyry  has  to  granite.  According  to 
the  mineral  of  the  phenocrysts  which  shows  predominantly, 
they  are  divided : 

(a)  Felsophyre  with  orthoclase  phenocrysts  is  quartzless 
orthoclase-^or^>\\yry,  or  quartzless  orthophyre. 

(b)  Felsophyre    with    phenocrysts   of   orthoclase,   horn- 
blende,  biotite,  and  augite,  syenite-porphyry. 

(c)  The  same   with   orthoclase  and   hornblende  is  horn- 
^^^-syenite-porphyry. 

(d)  The  same  with  orthoclase  and  biotite  is  ^'^^-syenite- 
porphyry. 

(e)  The  same  with  orthoclase  and  augite  is  ^^'/^-syenite- 
porphyry. 


154  MANUAL    OF  LITHOLOGY. 

IV0.  QUARTZLESS  ORTHOCLASE-POR- 
PHYRY,  Quartzless  Orthophyre  (according  to 
J.  D.  Dana). 

A  feldspathic  groundmass  in  which  only  potash-feldspar 
occurs  in  phenocrysts,  with  no  appearance  of  black 
bisilicates  except  as  (m)  in  the  groundmass,  where 
they  are  usually  altered  to  secondary  products,  such 
as  calcite,  chlorite,  and  hydrated  ferric  oxide. 
Contains  silica  56-62  ;  Gr.  2.55-2.60. 

It  occurs  in  dikes  and  sheets  in  the  Thuringian  Forest, 
Tyrol,  the  Balkans,  Scotland,  Greenland.  These  rocks  are 
separated  from  the  quartzless  felsite-porphyries  by  their 
lower  acidity.  The  groundmass  is  light  to  dark  through 
shades  of  red,  yellow,  gray,  and  green,  and  consists  almost 
entirely  of  (m)  feldspar  crystals  —  usually  orthoclase  —  with 
th£  alteration  products  of  the  black  bisilicates.  It  seems  to 
be  entirely  without  base,  and  holocrystalline.  The  glassy 
habit  of  the  feldspar  gives  it  frequently  a  trachytic  appear- 
ance. Orthoclase  is  milk-white,  yellowish,  or  reddish; 
plagioclase  is  almost  absent. 

i.  Rhomb  Porphyry  (L  v.  Buch).  From  Norway.  The 
light-violet  groundmass  carries  deep-gray  crystals  of  ortho- 
clase, which  give  rhombic  sections.  When  weathered  the 
mass  is  reddish.  It  is  compact  and  shows  (m)  orthoclase, 
augite,  magnesia-mica,  olivine,  and  magnetite.  Weathering 
affords  a  good  number  of  secondary  minerals,  as  carbonates 
quartz,  iron  ores,  from  the  chloritized  augite  and  biotite,  ser- 
pentine from  the  olivine,  and  sometimes  epidote  and  sericite. 
The  orthoclase  feldspar  is  sometimes  microcline,  and  some- 
times anorthoclase.  It  occurs  in  surface  sheets  and  dikes.  It 
contains  55-61  silica,  with  Gr.  2.61.  The  orthoclase  crystals 
are  sometimes  two  inches  long.  The  carrying  only  these 
phenocrysts  places  this  rock  under  the  orthophyres  ;  but 


PRIMARY  ROCKS.  155 

the  chemical  composition  places  only  the  more  acid  here,  the 
main  body  belonging  with  the  augite-syenite  porphyries. 

2.  KERATOPHYRE  (Giimbel). 

A  ( M)  compact  groundmass  resembling  hornstone 
(whence  the  name),  carrying  very  small  phenocrysts 
of  feldspar,  (m)  the  groundmass  is  fine  crystalline 
granular  and  composed  mainly  of  feldspar,  which 
somewhat  resembles  trachyte,  and  sometimes  ortho- 
phyre.  It  has  a  variable  quartz  content  which  is  (M) 
in  the  quartz  variety. 

Silica  6 1-66  ;  Gr.  2.61. 

QUARTZ-KERATOPHYRE  (Lossen). 
A  similar  rock  containing  a  large  amount  of  quartz  in 
the  groundmass  and  as  phenocrysts  in  small  number. 
The  groundmass  is  coarser  grained  than  in  the  basic 
variety.  It  occurs  at  Baraboo,  Wis.,  like  a  lava,  and 
associated  with  tuffs. 

Silica  70-80  ;  Gr.  2.64. 

The  basic  variety  occurs  in  the  Fichtelgebirge,  Harz, 
Nassau,  and  in  New  England  (see  below) ;  the  quartz  variety 
in  Saxony,  Great  Britain.  Both  are  soda-orthoclase  rocks, 
where  the  feldspar  is  sometimes  a  mixture  of  both  orthoclase 
-and  albite,  and  sometimes  microperthite.  The  phenocrysts 
.are  variable  from  few  to  abundant.  In  the  groundmass 
appear  also  (m)  grains  of  magnetite,  folia  of  brown  mica, 
.and  specks  of  hornblende.  (See  under  "  Quartz-porphyries  " 
p.  141). 

(a)  Bostonite  (Hunter  and  Rosenbusch).  From  Marblehead 
Neck,  Mass.,  Chateaugay  Lake,  N.  Y.,  the  Champlain  val- 
ley ;  Montreal,  Canada,  Norway,  Brazil,  as  basic  keratophyre 
in  dikes.  It  is  a  light-colored  rock,  with  rough  trachytic 
feel  on  a  fracture,  carrying  phenocrysts  of  orthoclase,  while 
the  groundmass  carries  the  same  with  anorthoclase.  It  is 


1 56  MANUAL    OF  LITHOLOGY. 

essentially  a  feldspathic  rock,  without  black  bisilicates,  and 
carrying  (Norway)  61  silica.  Brogger's  exhaustive  study  of 
the  associated  bostonites  and  comptonites  of  Gran,  Norway, 
conclusively  shows  that  they  are  differentiations  from  a 
gabbroitic  magma,  and  extrude  sometimes  at  the  same  time 
and  in  the  same  dike,  where  each  is  at  times  the  envelope 
of  the  other,  and  he  suggests  for  these  and  similarly  differ- 
entiated rocks  the  term  "  complementary,"  and  states  that 
they  should  be  classed  with  the  rock-form  of  the  undiffer- 
entiated  magma. 

IV£.  SYENITE-PORPHYRY. 

A  (M)  fine-grained  to  compact  groundmass  without 
base,  and  carrying  phenocrysts  of  orthoclase,  horn- 
blende, mica,  and  augite  at  the  same  time,  the  first 
predominating. 

The  groundmass  is  always  crystalline-granular  and  com- 
posed of  the  minerals  noted  above,  and  with  feldspar  greatly 
predominant.  They  weather  to  chlorite  and  carbonates.  As 
accessories  are  titaniferous  magnetite,  titanite,  apatite,  and 
zircon.  In  the  augitic  variety  olivine  is  also  accessory. 
They  occur  in  dikes,  and  are  distinguished  from  similar 
dioritic  porphyries  by  their  color,  their  freedom  from 
amygdaloidal  states,  and  their  having  orthoclase,  which  gives 
a  potash  rather  than  a  lime-soda  result  to  the  chemical 
analysis.  Quartz  may  be  sparingly  present  without  placing 
the  rock  among  the  quartz-porphyries.  As  varieties : 

I.  Hornblende-syenite-porphyry.  A  rock  found  in  dikes 
and  sheets,  of  compact  groundmass,  and  carrying  pheno- 
crysts of  orthoclase  and  hornblende.  The  groundmass 
shows  usually  all  the  syenitic  minerals,  and  the  black  bisili- 
cates weather  to  chlorite,  epidote,  and  calcite.  This 
changes  the  fresh  brown  or  reddish-brown  rock  to  green 
or  grayish  green.  It  contains  61  silica,  and  occurs  in  the 
Vosges,  Tyrol,  and  Black  Forest. 


PRIMARY  ROCKS.  1 57 

2.  Biotite- syenite -porphyry.      A   dike-rock   of   limited 
•extent  in   the   southern  Vosges,  Sweden,  Portugal.     It   is 
•deep  reddish  brown  when  fresh,  and  chloritizes  to  greenish 
-shades.    Augite  generally  accompanies  the  biotite,  and  more 
or  less  plagioclase  the  orthoclase. 

3.  Augite-syenite-porphyry.      A  similar  occurring  rock 
from  Brazil,  the  Caucasus,  Montenegro,  Spain,  Albany,  N. 
Y.     The  groundmass  is  greenish   gray,  and   composed  of 
large  proportions  of  plagioclase  with  the  orthoclase,  augite, 
magnetite,   pyrite,   and   altered   olivine.     The  phenocrysts 
are  usually  large   orthoclases   and  augites.     The  latter  is 
usually   dark   green,   but   at   Albany,    N.  Y.,   it   is   violet- 
brown  and  accompanied  by  a  bluish  amphibole.     Olivine 
.appears  sparingly. 

V.  COMPACT  SYENITE  (Kalkowsky),  Microsy- 
enite  (Wadsworth),  Syenite-aphanite  (Zirkel). 

A  compact  mixture  of  syenite  minerals  (sometimes  fine- 
granular),  of  dark  greenish  gray  color,  in  narrow  dikes,  and 
bearing  to  syenite  the  same  relation  that  felsite  does  to 
granite.  It  is  usually  weathered  and  the  black  bisilicates 
•cloritized  (which  accounts  for  the  color),  and  calcite  is 
sometimes  primary  and  sometimes  secondary.  This  is 
distinguished  from  syenite  by  the  failure  to  detect  by  the 
naked  eye  the  syenitic  minerals ;  but  the  lens  and  micro- 
•scope  show  them.  The  fineness  of  the  grain  is  peculiar  to 
dike-rocks  and  the  peripheries  of  larger  masses  where  the 
walls  are  somewhat  heated,  so  that  cooling  is  not  instantane- 
ous, but  more  rapid  than  in  the  center  of  large  masses. 
Wadsworth's  microsyenite  is  the  parallel  of  Rosenbusch's 
microgranite  of  similar  rate  of  cooling.  Aplite  is  of  like 
origin.  This  may  be  taken  as  the  groundmass  of  the  above 
syenite-porphyries,  and  is  associated  with  syenites  and  sye- 
nitic mica-traps. 

There  is  no  syenite  glass. 


MANUAL    OF  LITHOLOGY. 
GROUP    5.      PHONOLITE. 

PHONOLITE-EL&OLITE-SYENITE  EXTRUSIVES. 
(Necessary  minerals:   An  alkali   feldspar,   elaeolite,   or  nepheline,  and 

hornblende.) 

PHONOLITE  (Klaproth),  Clinkstone. 
A  (M)  compact  groundmass  which,  in  its  fresh  state,  is 
dark  greenish  or  yellowish  gray,  showing  sporadic 
individual  cleavage  surfaces  of  sanidine.  The  mass 
shows  a  great  tendency  to  fracture  like  slates  and 
schists,  or  is  thin  tabular-jointed.  Under  these  con- 
ditions it  gives  a  clear  sound  when  struck  with  a 
hammer  (whence  the  name).  On  weathering  a  sharply 
defined  yellowish-white  or  white  crust  is  formed, 
(m)  it  is  a  compound  of  sanidine  and  nepheline  (or 
leucite),  with  essential  nosean  (or  hauyne),  monoclinic 
pyroxene,  hornblende,  magnesia-mica  rarely,  and  still 
more  rarely  plagioclase.  The  last  seems  to  be  re- 
stricted to  trachytic  phonolites  poor  in  nepheline. 
This  is  divided  into  : 

(A)  TYPICAL    PHONOLITE,    or    Nepheline-tra- 

chyte  (Zirkel). 

A  compound,  as  above  described,  of  sanidine  and  nephe- 
line, with  the  other  minerals  as  accessories  only. 
Silica  50-62  ;  Gr.  2.4-2.65. 

Phonolite  occurs  generally  in  isolated  and  precipitous 
dome-shaped  masses  ot  large  size  (Fernando  do  Noronha), 
as  surface  sheets  of  great  extent,  as  lava-flows,  and  in 
dikes.  It  is  found  in  Great  Britain,  Germany,  Bohemia, 
central  France,  northern  and  eastern  Africa,  Cape  Verdes, 
Canaries,  Asia,  Paraguay,  Brazil,  the  Black  Hills,  and  (in 
loose  blocks)  in  Pasolty  County,  Col.  The  sanidine  is 
(m)  in  the  groundmass  and  (M)  as  large  tabular  phenocrysts,. 


PRIMARY  ROCKS.  1 59 

with  the  clinopinacoid  parallel  to  the  cleavage  plane,  and 
with  twinning  after  the  Carlsbad  type.  Anorthoclase 
occurs  (m).  Nepheline  is  generally  (m) ;  but  it  is  (M)  in 
some  Bohemian  types,  and  in  New  Zealand  it  occurs  in 
reddish  phenocrysts  one-half  by  one-fourth  of  an  inch  in  size. 
Nosean  is  (M)  occasionally,  and  hatiyne  rarely  ;  the  latter  has 
been  noted  3-4  mm.  long.  Sodalite  (which  has  been  mis- 
taken for  the  latter)  is  sometimes  2-3  mm.  long.  Plagioclase 
is  very  irregular  in  this  variety.  Hornblende  is  common  in 
(M)  black  needles  that  do  not  change  to  chlorite  or  epidote. 
Large  augite  phenocrysts  are  infrequent,  but  sometimes  7 
mm.  long.  Part  of  these  approach  aegirite,  which  occurs 
(m).  Great  brown  folia  of  magnesia-mica  occur  sparingly 
in  a  few  localities.  Magnetite  is  constant,  but  (m).  Honey- 
yellow  titanite  (also  yellowish  red)  is  abundant  (M);  also 
zircon  1-2  mm.  long.  Olivine  is  wanting  as  a  characteristic 
mineral;  but  occasionally  it  is  found,  and  sometimes  2-15 
mm.  long.  Quartz  and  tridymite  are  scarce  and  (m).  Zirkel 
states  that  the  groundmass  is  of  two  kinds,  a  typical  phono- 
litic  and  a  trachytic  state.  The  former  is  dark-colored,  with 
greasy  luster,  compact  and  non-porous,  except  as  small 
haiiyne  or  nepheline  crystals  have  been  removed  by 
weathering  ;  with  ready  cleavage,  and  small  phenocrysts,, 
which  are  generally  sanidine.  The  cleavage  is  less  marked 
in  the  highly  porphyritic  states.  The  groundmass  fuses 
bp.  more  or  less  readily  to  a  yellowish  or  greenish  glass, 
and  gives  water  in  the  closed  tube.  This  type  is  found  in 
Bohemia,  the  Mittelgebirge,  the  Lausitz,  Cornwall  (Wolf 
Rock),  central  France,  Teneriffe,  and  the  Canaries.  The 
groundmass,  of  trachytic  habit,  is  cleavable  with  difficulty  or 
not  at  all ;  luster  sub-greasy ;  color  generally  light-gray  or 
yellowish  gray  ;  of  rough  porous  feel.  In  rare  cases  small 
phenocrysts  of  nepheline  appear  with  plagioclase.  This 
is  found  in  the  Rhone  district  and  Bohemia,  and  must 


MANUAL    OF  LIT  HO  LOG  Y. 

be  distinguished  from  the  old  so-called  "  trachytic  phono- 
lite,"  which  had  lost  its  cleavage  from  weathering.  The 
groundmass  is  partly  soluble  in  HC1,  the  soluble  part 
being  nepheline  and  zeolites,  while  the  feldspathic  part  is 
insoluble.  The  specific  gravity,  and  the  percentages  of 
soluble  matter  and  of  water,  are  inversely  proportionate  to 
the  percentage  of  silica.  The  cleavable  states  generally 
split  readily  and  in  thin  sheets,  so  that  the  rock  can  be  used 
for  slating  (Cantal  in  central  France).  Whole  mountains 
of  phonolite  are  divided  by  joints  one  foot  apart.  It  also 
separates  into  long  prisms,  but  not  with  such  regularity 
as  in  basalt.  The  cleavages  seem  to  be  parallel  to  the  cool- 
ing surface,  and  the  prisms  perpendicular  to  the  same. 
Phonolite  weathers  with  a  sharply  defined  grayish-white  to 
yellowish-white  crust,  which  at  first  adheres  to  the  tongue. 
Zirkel  states  that  the  minerals  are  removed  in  the  following 
order:  magnetite,  hauyne,  sodalite,  the  glass  base  (if  pres- 
ent), and  nepheline.  All  form  zeolites,  which  next  go,  and 
leave  hornblende,  augite,  and  sanidine.  After  the  alteration 
of  the  bisilicates  the  feldspar  kaolinizes  after  prolonged 
weathering,  to  form  a  gray  or  mottled  clay.  Other  states 
are  as  follows : 

(a)  Porphyritic  Phonolite.  Though  the  rock  is  generally 
porphyritic,  there  is  now  and  then  a  specially  porphyritic 
state,  as  in  Bohemia,  the  Rhone  district,  etc.  It  is  a  (m) 
fine-grained  aggregate  of  phonolitic  minerals,  rich  in  horn- 
blende, with  either  an  abundance  of  large  hornblende 
prisms  (sometimes  5  cm.  long),  an  aggregate  of  hornblende 
and  titanite,  or  a  mixture  of  light-yellow  transparent  titan- 
ite,  black  hornblende,  mica,  nepheline,  and  zircon,  which  is 
like  the  allied  rock  at  Ditro. 

(ft)  Vesicular  Phonolite  is  reported  from  Blattendorf,  near 
Haida,  Bohemia. 

(c)  Spotted  Phonolite  is  only  a  colored  state  due  to  local 


PRIMARY  RGCKS.  l6l 

decomposition,  at  Luschwitz,  near  Aussig,  Bohemia ;  or  to 
a  more  coarse  agglomeration  of  the  mineral  ingredients  in 
patches,  as  on  one  of  the  Cape  Verdes. 


PHONOLITE   GROUP   B.      (Zirkel.) 

Nosean  -  trachyte  (Lenk),  Haiiyne  -  trachyte,  Nosean- 
phonolite  (Zirkel). 

A  variety  of  phonolite  in  which  nepheline  is  replaced  by 
nosean  (haiiyne),  of  a  deep-black  color,  splintery  fracture, 
thin  jointed  structure,  and  gray  weathered  state.  The 
groundmass  is  compact,  and  shows  (M)  only  sporadic  long 
prisms  of  hornblende ;  but  (m)  exhibits  sanidine,  augite, 
magnetite,  and  abundance  of  minute  nosean.  Plagioclase 
and  nepheline  seem  to  be  absent.  It  occurs  in  loose  blocks 
at  the  Kreuzberg,  Mont  Dore,  in  northern  Bohemia,  in  a 
dike  at  La  Rochette,  etc. 

Taimyrite  (v.  Chrustschoff).  From  Taimyr  Land, Siberia. 
An  ophitic  aggregate  of  nosean  and  anorthoclase,  with  ac- 
cessory plagioclase,  amphibole,  biotite,  melanite,  magnetite, 
sphene,  zircon,  and  glass.  Anorthoclase  is  in  long  slender 
crystals  and  nosean  abundant.  Zircon  is  the  only  accessory 
of  importance  and  is  of  trachytic  type.  Associated  with 
this  is  a  similar  compound,  except  that  sodalite  replaces 
nosean,  and  that  zircon  is  granitic.  Gr.  2.57-2.62.  The  rock 
is  nearly  ophitic. 


l62  MANUAL   OF  LITHOLOG  Y. 

PHONOLITE   GROUP  C.      (Zirkel.) 

LEUCITE  -  PHONOLITE,    Leucite-nepheline-tra, 

chyte      (Zirkel),  Leucitophyre  (Rosenbusch). 
A  microcrystalline  groundmass,  with  a  small  amount  of 
glass,  carrying  phenocrysts  of  sanidine,  leucite,  nephe- 
line,  and  haiiyne  (colorless,  bluish  gray  to  black,  or, 
when  weathered,  white  or  reddish),  hornblende,  and 
no  plagioclase  nor  olivine. 
Silica  45-54 ;  Gr.  2.5-2.9. 

It  is  found  in  loose  blocks,  in  plugs,  in  tuff,  also  in  dikes 
near  the  lake  of  Laach,  Rieden,  Selberg,  etc..  in  Bohemia,, 
Italy,  Persia,  etc.  The  groundmass  consists  (m)  of  a  small 
amount  of  glass  base  with  an  abundance  of  crystallized 
sanidine,  leucite,  nepheline,  hauyne,  augite,  biotite,  horn- 
blende, titanite,  apatite,  magnetite,  and  melanite.  Some 
occurrences  are  porous.  By  weathering  calcite  and  zeolites 
appear,  and  analcite  forms  pseudomorphs  after  the  leucite. 

(a)  Nosite-melanite  Rock  (vom  Rath).  A  fine-grained  to 
compact  compound  of  leucite,  nepheline,  nosite,  sanidine, 
black  garnet  (melanite),  with  some  hornblende,  pyroxene, 
and  titanite.  Contains  silica  48-5  5;  Gr.  2.7-2.9.  This  is  a 
grayish  dark-colored  rock  that  frequently  shows  hyalite 
crusts,  from  the  decomposition  of  the  silicates  it  contains. 

PHONOLITE   GROUP   D.      (Zirkel.) 

LEUCITE-TRACHYTE  (vom  Rath). 
In  a  compact  light-gray,  bluish-gray,  or  dark-gray  ground- 
mass,  with  splintery  fracture,   occur   fresh  sanidine, 
white  and  somewhat  decomposed  leucite,  blue  hauyne, 
augite,  mica,  magnetite,  and    seldom    titanite.     The 
vesicular  cavities  are  filled  with  (m)  small  nephelines. 
Silica  60. 

This  occurs  in  a  few  places  in  Italy  and  Brazil  in  lava- 


PRIMARY  ROCKS.  163 

streams.  The  leucite  appears  to  be  as  phenocrysts,  and 
does  not  show  in  the  groundmass  to  any  extent.  This  latter 
is  macrocrystalline.  The  leucites  are  sometimes  10  cm. 

(a)  Olivine-leucite-phonolite  (A.  Hague).  As  detritus  in 
the  Ishawooa  River,  Wyoming,  consisting  of  numerous 
phenocrysts  of  olivine  and  augite  in  a  groundmass  com- 
posed (m)  only  of  leucite  and  an  alkali  feldspar,  with  a  small 
showing  of  plagioclase  and  folia  of  biotite. 


PHONOLITE  GLASS. 

As  stated  at  the  beginning  of  the  rocks,  the  tendency  to 
form  hyaline  states  decreases  with  the  lowering  of  the  con- 
tent of  silica  in  a  rock,  and,  at  the  same  time,  the  tendency 
to  crystallize  increases.  There  may  be  numerous  instances 
of  glassy  states  of  this  rock,  but,  as  yet,  few  have  been 
noted.  They  have,  probably,  long  since  been  removed  by 
erosion,  as  phonolite  is  not  found  in  very  recent  effusions. 

Phonolite-pitchstone  (Laube).  Near  Weipert  is  a  brownish 
black  rock,  of  pitchy  luster  and  fluidal  structure,  in  which 
are  (m)  numerous  phenocrysts  of  sanidine,  magnetite,  and 
nepheline. 

Phonolite-obsidian.  As  selvages  to  phonolite  dikes  and 
lava-streams  in  Teneriffe  ;  in  phonolite  tuffs,  and  as  volcanic 
bombs,  with  silica  73.  It  is  black,  gelatinizes  with  HC1, 
and  gives  crystals  of  NaCl.  (m)  it  shows  sanidine,  aegirite, 
and  Tiaiiyne,  with  chalcedonic  nepheline. 

Leucite-phonolite-pumice.  In  minute  fragments  in  a  tuff 
of  this  rock  at  the  foot  of  the  Olbruck.  They  show  an 
almost  colorless  foamy  glass  with  sharply  defined  (m) 
phenocrysts  of  leucite,  augite,  nepheline,  rarely  hauyne, 
magnetite,  or  titanite,  and  as  the  arrangement  is  the  same 
as  in  the  rock  of  the  Olbruck,  it  is  accepted  as  a  true  phono- 
lite-pumice. 


164  MANUAL    OF  LITHOLOGY. 

GROUP   6.     EL^OLITE-SYENITE. 
PHONOLITE-EL&OLITE-SYENITE  INTRUSIVES. 
(Necessary  minerals  :  Alkali  feldspar,  elaeolite,  and  hornblende.) 

EL^OLITE-SYENITE. 

A  compound  of  an  alkali  feldspar,  elaeolite  (leucite,  etc.), 
one  of  the  black  bisilicates,  and  no  quartz. 
Silica  43-68  ;  Gr.  2.46-2.63. 

This  rock  occurs  in  extended  masses,  bosses,  laccoliths, 
and  dikes,  like  syenite,  and  is  also  found  in  erratic  blocks 
(probably  distributed  through  glacial  agencies).  It  is  found 
in  the  Tyrol,  Portugal,  Pyrenees,  Transylvania,  southern  Nor- 
way, Sweden,  Lapland,  Ilmen  Mountains,  Greenland,  Brazil, 
Africa,  the  Cape  Verdes,  Great  Britain,  and  'in  North 
America  in  eastern  Ontario,  and  near  Montreal,  Canada  ;  at 
Salem  and  Marblehead,  Mass. ;  Red  Hill,  N.  H. ;  Litchfield, 
Me. ;  Magnet  Cove  and  elsewhere  in  Arkansas ;  Beemers- 
ville,  N.  J. ;  through  the  Champlain  valley  of  Vermont  ;  in 
New  York ;  Trans-Pecos  region,  Tex.  ;  Crazy  Mountains, 
Mont.,  and  Rocky  Mountains  of  Canada.  It  occurs  massive, 
schistose,  and  porphyritic,  as  follows : 
I.  Elaelite-syenite. 

(a)  Z^^-elaeolite-syenite. 

(b)  J/^/tfwzV^-elseolite-syenite. 
II.  Monchiquite. 

III.  Elasolite-syenite-/0r/^/rj/. 

(a)  Z^a/^-elasolite-syenite-porphyry. 

I.  EL^EOLITE-SYENITE,  Laurdalite  (Brogger). 

A  generally   light-colored  granitoid  compound,  varying 
from  medium  fine-grained  to  irregular  coarse-grained, 
of  an  orthoclase,  amphibole,  mica  (mostly  biotite),  and 
pyroxene,  with  quartz  almost  always  absent. 
Average  silica  53  ;  Gr.  2.55. 

This  is  a  smutty  red  (M)  compound  of  variable  mixture ; 


PRIMARY  ROCKS.  1 $ 

at  times  regularly  or  irregularly  coarse  granitoid  ;  at  times 
trachytic  from  tabular  minerals ;  at  times  with  parallel 
arrangement  of  the  minerals  as  in  phonolite.  Fluidal  struc- 
tures show  (m).  Orthoclase  forms  stout  crystalline  grains 
with  Carlsbad  twins  (rarely  of  Baveno) ;  often  microper- 
thitic.  Sometimes  microcline,  anorthoclase,  and  crypto- 
perthite  are  present ;  also  plagioclase  in  varying  amount. 
Elasolite  is  generally  idiomorphic  with  respect  to  feldspar, 
and  occurs  crystal,  and  in  irregular  grains  of  whitish, 
grayish,  reddish  color,  and  sometimes  2J-  feet  long.  It  alters 
to  Ca-Na-zeolites  and  calcite.  Melanite  is  sometimes  found 
(m).  Well-crystallized  blue  sodalite  is  common.  Cancrinite 
is  present  as  a  primary  and  as  an  alteration  product.  Leu- 
cite  is  not  present,  but  represented  by  analcite.  Pyroxene 
is  usually  green  and  well-crystallized  augite,  which  is  some- 
times epidotized  ;  sometimes  colorless  malakolite  is  found  in 
fine-grained  rocks,  sometimes  aegirite  in  radial  aggregates, 
sometimes  both  augite  and  segirite  together  ;  brown  acmite 
(at  Beemersville,  N.  J.)  occurs,  to  the  exclusion  of  the  others. 
Rosenbusch  says  that  pyroxene  sometimes  fails  entirely. 
Hornblende,  as  should  be  the  case,  is  the  most  constant  of  the 
black  bisilicates,  and  when  two  are  together  one  is  generally 
this  mineral.  It  occurs  green,  brownish  green  (by  trans- 
mitted light),  and  generally  idiomorphic.  It  is  usually  a 
soda-hornblende,  as  shown  by  the  flame,  ^nigmatite  some- 
times occurs  in  long  individuals.  Mica  is  generally  biotite 
(dark-brown  magnesia-mica)  in  hexagonal  tables  and  irregu- 
lar folia  ;  sometimes  it  is  dark  green.  Lepidomelane  occurs 
in  black  lustrous  tables  at  Litchfield,  Me.  Nosean  is  found 
now  and  then.  The  common  accessories,  magnetite  (ordi- 
nary and  titaniferous)  and  apatite,  are  (m) ;  calcite  is  com- 
mon as  secondary,  zeolites  less  so ;  eudyalite  (M)  is  rare  ; 
melanite,  nosean,  and  wollastonite  are  (m)  at  Montreal; 
scapolite  (M)  in  eastern  Ontario;  zircon  is  sporadic* (the 


1 66  MANUAL   OF  LITHOLOGY. 

so-called  "zircon-syenite"  of  Norway  is  an  elasolite-syenite 
rich  in  the  mineral) ;  olivine  and  pyrite  sometimes  occur. 
This  rock  seems  to  be  a  middle  ground  on  which  all  the 
other  varieties  meet.  The  sporadic  and  scanty  quartz,  with 
orthoclase,  sometimes  causes  a  resemblance  to  granite: 
nepheline  and  leucite  (also  melanite),  with  an  increase  of 
plagioclase  and  the  black  bisilicates,  ally  it  to  the  basic 
rocks;  while  a  predominance  of  the  latter  minerals  places 
it  at  their  most  basic  end,  as  is  shown  by  the  great  range  of 
its  silica  content.  We  can  distinguish 

I.  Hornblende -pyroxene-elasolite-syenite,  where  the  two 
black  bisilicates  are  equally  predominant.  The  varieties 
are: 

(a)  Foyaite  (Blum).  From  the  mountains  Foya  and 
Picota  in  the  province  of  Algarve,  Portugal.  A  granitoid 
compound  of  orthoclase,  elasolite,  hornblende,  pyroxene, 
and  biotite.  Orthoclase  is  prominent  in  white  or  grayish 
white  elongated  tables  with  imperfect  twinning  ;  plagioclase 
is  accessory ;  reddish  and  weathered  elasolite  in  hexagonal 
crystals ;  pyroxene  (augite  and  aegirite)  in  green  crystals ; 
green  hornblende ,  biotite  in  hexagonal  folia.  As  accesso- 
ries apatite  and  magnetite  are  constant  and  abundant ;  soda- 
lite  and  titanite  sporadic  ;  melanite,  tourmaline,  and  pyrite 
occasional ;  rarely  cancrinite,  epidote,  or  zeolites.  The 
texture  varies  rapidly  from  fine  to  coarse,  but  the  crystals 
are  usually  equidimensional.  It  is  sometimes  compact  and 
porphyritic,  but  without  base,  and  of  ash-gray  color.  The 
content  of  black  bisilicates  varies  greatly  ;  generally  pyrox- 
ene is  predominant,  sometimes  it  is  alone  ;  sometimes  horn- 
blende is  alone,  and  sometimes  accompanied  by  mica — all  in 
the  same  mass.  The  Libertyville  (N.  J.)  rock  carries  yel- 
lowish orthoclase  two  inches  long,  abundant  elasolite,  aegir- 
ite, and  sodalite,  while  biotite  is  rare.  Brogger  gives  this 
name  to  a  trachytoid  rock  in  Norway  with  a  different  com- 


PRIMARY  ROCKS.  1 67 

position.  (Here  would  come  the  coarse-grained  and  trachy- 
toid  states  of  the  Brazilian  rock  whose  dike-forms  are 
called  tinguaite  (Rosenbusch),  as  Hussak  states  that  this 
rock  is  only  a  porphyritic  state  of  foyaite.  In  the  United 
States  there  is  the  same  variation  in  the  values  of  the  horn- 
blende and  pyroxene  content,  as  well  as  the  same  changes 
in  structure  of  the  principal  mass.) 

(b)  Cancrinite-agirite-syzmtQ  (Tornebohm).     From    the 
Siksjoberge,  Sweden,  in  dikes  and  masses — the  former  are 
porphyritic.     It   consists   of    tabular   feldspar   (orthoclase, 
anorthoclase,    microcline,    and   plagioclase),    cancrinite   in 
crystals  f  inch  and  in  irregular  grains,  in  a  (ni)  mixture  of 
the  same  with  elseolite,  aegirite,  titanite,  and  apatite.     (See 
later  under  "  Elseolite-syenite-porphyry.") 

(c)  Sodalite-syzmtt  (Steenstrup).     From  Julianshaab  dis- 
trict, Greenland.     A   light  yellowish-gray,  coarse-grained, 
miarolitic  granitoid  principal  mass  of  greenish-white  lath- 
shaped  feldspar  (microcline,  -J  inch  long),  black  arfvedson- 
ite  (9  inches  long  by  3^  inches  thick),  asnigmatite,  aegirite 
(with  submetallic  luster),  and  sodalite  (i  inch  thick).     Gar- 
net, red  eudialyte,  and   infrequent  elseolite  are  accessory, 
and  sometimes  £  inch  thick.     Silica  56.45. 

2.  Mica-elaeolite-syenite,  Miascite  (G.  Rose).  From 
Miask  in  the  Urals.  Composed  of  orthoclase  (Breithaupt's 
microcline),  white  or  gray  ;  yellowish-white  elaeolite  with 
subresinous  luster  ;  gray  to  blue  sodalite  ;  nearly  equiaxial 
leek-green  mica.  As  accessories,  wohlerite,  zircon,  ilmenite 
3i  by  2\  inches,  cancrinite,  pyrite,  monazite,  quartz,  horn- 
blende, and  pyrochlore.  It  is  also  found  near  Lake  Superior. 
Silica  68.16. 

(a)  Litchfieldite  (Bayley).  From  Litchfield,  Me.  It  shows 
snow-white  feldspar  (orthoclase,  albite,  microcline),  large 
yellowish  cancrinite,  dark-blue  allotriomorphic  sodalite, 
gray  greasy  elasolite  (2  inches),  black  loha  of  lepidomelane, 


1 68  MANUAL    OF  LITHOLOGY. 

and  sometimes  brown  zircon.     Hornblende,  pyroxene,  and 
titanite  are  absent.     Silica  60.39. 

(b)  Pulaskite  (J.  F.  Williams).  From  Pulaski  and  neigh- 
boring counties,  Ark.  A  porphyritic  compound  of  biotiter 
orthoclase,  cryptoperthite,  scanty  elaeolite,  arfvedsonite,  and 
diopside.  The  phendcrysts  are  orthoclase.  Silica  60.03. 

3.  Hornblende-mica-elaeolite  -  syenite,  Ditroite.  From 
Ditro  in  the  Siebenburgen  in  Transylvania.  A  coarse-  to 
fine-grained  rock — somewhat  finer  grained  than  miascite — 
with  occasional  compact  and  schistoid  states.  The  parallel 
arrangement  of  sodalite  adds  to  this  last  effect.  It  contains 
white  orthoclase  (weathering  red),  microcline,  plagioclase, 
gray  elaeolite,  large  (i  inch)  prisms  of  hornblende,  usually 
altered  to  chlorite  or  biotite,  blue  sodalite,  and  usually  can- 
crinite.  Titanite  and  zircon  are  abundant  accessories. 
Secondary  products  are  muscovite,  calcite,  chlorite,  epidote, 
and  ferrite. 

(a)  Zircon- syenite.     A  variation  of  the  last  with  abundant 
zircon.     Where  it  has  been  described  as  a  separate  rock,  it 
is  a  granitoid  compound  of  orthoclase,  microcline,  elasolite, 
occasional   sodalite,  abundant  zircon  (red,  brown,  yellow), 
and  scanty  hornblende.     It  occurs  in   Norway,  at  Marble- 
head,  Mass.,  etc.     Silica  50-55  ;  Gr.  2.7-2.9. 

(b)  Endyalite-syemte   (Vrba).      From   south   Greenland, 
composed  of  soda-orthoclase,  much  plagioclase,  yellowish 
white  elaeolite,   black  hornblende,  eudyalite  (in   blood-red 
grains  i  mm.),  magnetite,  apatite  and  small  nests  of  mica. 

la.  LEUCITE-elaeolite-syenite  (Hussak). 
A  coarse-grained  variety  from  Serra  de  Caldas,  Brazil, 
carrying  analcite,  which  is  pseudomorphed  after  leu- 
cite.  A  similar  rock  is  found  at  Magnet  Cove,  Ark. 
There  is  no  rock  yet  known  where  leucite  entirely 
replaces  elaeolite,  and  where  it  remains  unaltered. 


PRIMARY  ROCKS.  169 

\b.  MELANITE-elseolite-syenite,  Borolanite  (Home 

and  Teall). 

A  similar  rock  in  intrusive  sheets  and  dikes  near  Lake 
Borolan,  Assynt,  Scotland  (whence  the  name).  A 
medium-grained  mixture  of  soda-orthoclase  and  mel- 
anite  (with  pitchy  luster)  mixed  with  what  is  probably 
amorphous  elseolite,  green  pyroxene,  dark  biotite,  and 
a  sodalite  mineral.  Some  varieties  of  the  mass  have 
little  or  no  melanite,  but  consist  of  feldspar  and 
pyroxene. 

(Schistoid  Elaeolite-syenite.  This  is  not  a  variety,  but  a 
state,  of  this  rock  which  is  found  in  many  localities — notably 
at  Ditro,  near  Christiania,  and  in  Greenland,  and  is  due  to 
the  parallel  arrangement  of  the  minerals,  especially  the 
black  bisilicates.  There  are  also  lenticular  concretions, 
which  make  "pudding"  varieties  of  the  various  rocks. 
These  latter  are  caused  (as  in  granite)  by  aggregates  of  feld- 
spar and  elaeolite  with  some  of  the  black  bisilicates.) 


II.  MONCHIQUITE  (Hunter  and  Rosenbusch). 
A  dike-rock  associated  geologically  and  mineralogically 
with  the  elasolite-syenites,  and  having  a  distinct 
facies.  It  is  a  porphyritic  combination  of  augite  and 
olivine,  with  a  glassy  base,  with  which  may  be  asso- 
ciated either  hornblende  or  mica  (or  both  together). 
The  base  includes  (m)  phenocrysts  of  plagioclase  and 
occasionally  of  nepheline.  The  rock  is  black  or  gray- 
ish black  when  fresh,  and,  weathers  sharply  to  brown. 
It  gelatinizes  slightly  in  cold,  readily  in  hot,  HCL 
This  and  its  greasy  luster  are  indications  of  nephe- 
line. 

Silica  43-47  ;  Gr.  2.8-3.     Rosenbusch  divides  the 
species  thus : 


MANUAL    OF  LITHOLOGY. 

1.  With  olivine ; 

(a)  and  augite,  monchiquite ; 

(b)  and  augite  and  amphibole,  amflfa&ote-monchiquite  ; 

(c)  and  augite  and  biotite,  £*i/*/*-monchiquite ; 

(d)  and  augite,  amphibole,  and  biotite,  amphibole-b\ot\te- 

monchiquite. 

2.  Without  olivine. 

The  combinations  (a),  (b},  etc.,  are  as  just  stated. 

(a)  Fourchite  (J.  F.  Williams). 

(b)  Amphibole-iourchite  (Rosenbusch). 

(c)  Ouacliitite  (Kemp). 

(d)  Amphibole-ou2iC\i\\.\tQ  (Rosenbusch). 

The  name  comes  from  the  Serra  de  Monchique,  Portugal, 
where  the  first  of  the  type  was  found.  These  rocks  are  an 
entirely  (m)  series,  and  cannot  be  told  in  many  cases  from 
basalt,  except  by  their  brown  weathering.  This  and  the 
gelatinization  with  HC1  afford  some  chances  of  detection 
(M).  In  the  United  States  are  found 

Fourchite  (Fourche  Mountains,  Ark.;  Beemersville, 
N.  J.;  Essex  County,  N.  Y.;  Lake  Merpphremagog,  Vt.; 
Angel's  Island,  San  Francisco  Bay,  Cal.).  Silica  47. 

Ouachitite  (throughout  Arkansas,  Beemersville,  N.  J.). 
Silica  36.40. 

Monchiquite  (in  the  Lake  Champlain  region  of  Vermont). 

PORPHYRIES   OF  THE   EL^EOLITE-SYENITE   GROUP. 

III.  EL^EOLITE-SYENITE-PORPHYRY. 

A  more  or   less   compact   groundmass,  like  hornstone, 
with    subconchoidal  "or    splintery    fracture;    greasy 
luster ;  color  light  or  dark  green ;    carrying  pheno- 
crysts  of  feldspars,  elseolite,  and  sodalite. 
Silica  44-56;  Gr.  2.55. 

It  occurs  mainly  massive  and  in  dikes,  associated  with 


PRIMARY  ROCKS.  I /I 

the  crystalline  states.  It  is  found  in  the  Tyrol,  Greenland, 
Norway,  Brazil,  Portugal,  Scotland,  Montana,  Beemers- 
ville,  N.  J.  It  bears  to  elasolite-syenite  the  same  relation 
that  quartz-porphyry  does  to  granite. 

1.  Liebnerite-porphyry.     From  the  southern  Tyrol. 
Gieseckite-porphyry.     From  Greenland. 

In  weathered  dikes.  A  flesh-red  to  brown  groundmass 
(from  ferrite)  carrying  (m)  tabular  brick-red,  Carlsbad- 
twinned  orthoclase  phenocrysts,  and  J-inch  prisms  of  greasy 
oil-green  to  bluish  green  liebnerite  (geiseckite).  This  latter  is 
.a  micaceous  secondary  product  from  elaeolite.  Silica,  44.66. 

2.  Hornblende-pyroxene-elseolite-syenite-porphyry. 

(a)  Tinguaite  (Rosenbusch).  Dike-rocks  from  the  Serra 
de  Tingua,  Brazil,  similar  to  foyaite.  Hussak  states  that 
these  have  a  gneissoid  habit. 

3.  Nepheline-rhomb-porphyry  (Brogger).    In  a  dike  from 
•elaeolite-syenite  in  southern  Norway,  with  56-57  silica.     A 
somewhat  dark-grayish  to  violet  rock  with  (m)  fine-grained 
groundmass  carrying  large  phenocrysts  of  soda-orthoclase 
;and  microperthite.     The  groundmass  (m)  shows  nepheline. 
It  cannot  be  distinguished   from   rhomb  porphyry  by  the 
naked  eye,  but  HC1  reactions  will  show  difference. 

Ilia.  LEUCITE-elseolite-syenite-porphyry.  From 
Serra  de  Tingua,  Brazil,  and  with  pseudomorphs 
of  analcime  after  leucite — like  the  granular  rock. 

(Some  authorities  note  a  leucite-syenite-^Qrphjrj  contain- 
ing sanidine  and  what  appear  to  be  minute  (m)  orthoclases 
in  the  groundmass,  on  the  ground  of  its  being  a  Silurian 
extrusion,  and  state  that  it  would  be  a  phonolite  if  it  had  been 
extruded  as  late  as  Tertiary  times.  As  there  is  no  good 
reason  for  dividing  rocks  according  to  geological  age,  this 
rock  is  a  phonolite,  no  matter  whether  it  belong  to  pre-Cam- 
brian  or  recent  times.) 


INTERMEDIATE  DIVISION. 
II.  ALKALI-LIME-SODA  SECTION. 

MICA-TRAP  INTRUSIVES. 
(Necessary  minerals:  Feldspar,  black  bisilicates.) 

MICA-TRAP  ROCKS  (v.  Cotta),  LAMPROPHY- 
RES  (Rosenbusch). 

Naumann  first  used  the  name  "mica-trap"  for  a  rock  in 
the  Erzgebirge,  which  he  afterwards  identified  with  the 
"  minette  "  of  the  miners  of  the  Vosges,  and  in  1838  aban- 
doned the  old  name.  The  name  signified  a  rock  with  pre- 
dominant mica  that  resembled  "  trap  "  in  its  jointing  and 
weathering.  In  his  treatise  on  lithology  v.  Cotta  refers  to 
the  above  and  says :  "  Under  the  circumstances  it  may  be 
admissible  to  transfer  the  name  of  mica-trap  to  an  entire 
group  of  similar  rocks,  whose  common  attributes  are  that 
they  consist  principally  of  compounds  of  mica  and  feldspar, 
without  marked  porphyritic  texture,  and  that  they  contain 
no  quartz,  unless  quite  exceptionally.  We  count  in  this 
group  the  following  rocks  (although  it  is  uncertain  if  they 
all  are  of  igneous  origin),  viz.,  minette,  fraidronite,  kersan- 
ton,  and  kersantite.  Until  that  question  is  determined  in 
the  negative  they  may  be  so  classed  on  account  of  their 
petrographic  affinity  ;  and  for  the  same  reason  they  will  be 
most  conveniently  treated  as  varieties  of  the  same  rock." 

Eight  years  after  this  was  issued  Gumbel  described  his 
lamprophyre,  and  twenty-one  years  after  the  same  date 
Rosenbusch  gathered  the  above  rocks  into  the  class  of 

172 


PRIMARY  ROCKS.  173 

**  lamprophyres,"  which  differed  from  the  original  "diabase 
like  "  rock  of  Giimbel  in  having  orthoclase  as  one  of  the 
constituents.  It  was  at  once  seen  that  these  rocks  could  not 
be  united  under  the  present  system  of  mineral  compounds, 
and  the  "  syenitic' '  and  "  dioritic  "  divisions  of  the  lampro- 
phyres  followed.  Zirkel  discards  the  later  name  entirely, 
and  places  minette  with  the  syenitic  porphyries,  and  the 
other  three  under  the  diorites.  All  of  them  show  to  a  con- 
siderable degree  the  columnar  and  tabular  jointing  and 
spheroidal  weathering  of  basalt,  the  original  "  trap  ";  and  as 
both  v.  Cotta  and  Rosenbusch  think  them  worthy  of  a 
separate  classification,  they  should  be  called  by  the  older 
name.  The  variation  in  their  feldspars,  however,  requires 
that  they  be  placed  under  the  syenitic  and  dioritic  groups, 
as  there  is  no  good  reason  for  separating  dike-rocks  from 
other  eruptives.  The  original  lamprophyre  of  Gumbel  was 
placed  by  him  with  the  mica-traps  (minette,  kersantite,  ker- 
santon,  and  mica-diabase),  and  the  name  "  shining  "  refers  to 
the  mica  content.  If  it  be  proper  to  annex  to  this  group  a 
rock  like  vosgesite,  which  is  conspicuous  for  having  little 
mica,  it  is  a  matter  of  little  consequence  whether  the  name 
of  the  group  be  "  lamprophyre  "  or  "  mica-trap,"  as  long  as 
both  refer  to  the  same  mineral.  The  lamprophyres  of  the 
Shap  granite  mass  in  England  are  shown  by  their  containing 
the  same  quartz,  orthoclase,  and  sphene  to  have  originated 
in  the  same  magma  as  the  granite  by  differentiation. 

These  rocks  may  be  imagined  to  be  granite-porphyries 
Door  in  quartz  and  rich  in  black  bisilicates.  They  can  be 
divided  according  to  their  feldspar : 

I.  With  an  alkali  feldspar,  syenitic  mica-trap. 

II.  With  plagioclase,  dioritic  mica-trap. 


MANUAL   OF  LITHOLOGY. 

GROUP  7.     SYENTIC   MICA-TRAP. 

I.    SYENITIC    MICA-TRAP,    Syenitic     Lampro- 

phyre  (Rosenbusch). 

A  series  of  porphyritic  rocks  (and  also  porphyries) 
having  a  (M)  fine-grained  to  compact  groundmass  of 
orthoclase  and  plagioclase  in  needles,  with  the  other 
syenitic  minerals  highly  predominant,  and  carrying 
some  or  all  of  them  as  phenocrysts.  Biotite  is  always 
present  in  the  groundmass  and  usually  as  phenocryst. 
They  can  be  taken  as  intermediate  between  the  syen- 
ites and  their  porphyries. 

Silica  48-65  ;  Gr.  2.5-2.9. 

These  are  a  series  of  dike  varieties  of  mica-syenite,  or 
states  that  have  cooled  under  similar  circumstances,  and 
they  differ  from  the  mica-porphyrites  in  the  state  of  the 
matrix  and  the  fact  that  the  mica  is  in  folia  rather  than  in 
tabular  crystals.  They  are  characterized  by  columnar  and 
tabular  jointing,  by  spheroidal  weathering,  and  by  resistance 
to  disintegration.  They  carry  as  accessories  magnetite, 
pyrite,  abundant  apatite,  and  the  derivatives  of  their  com- 
ponents. Under  this  head  will  be  grouped  : 

I.  Minette  (orthoclase  and  predominant  biotite). 

II.  Vosgesite  (Rosenbusch),  (orthoclase,  hornblende,  and 
augite). 

I.  MINETTE  (old  mining  name;  first  noted  by  filie 

de  Beaumont). 

In  a  matrix  usually  coarse  enough  to  be  resolved  by  the 
lens  (generally  fine  crystalline  and  porous,  with  dark- 
gray  color  (also  reddish  to  blackish-brown]);  com- 
posed of  orthoclase  and  much  mica  with  some  horn- 
blende, are  abundant  folia  of  biotite,  with  occasional 
phenocrysts  of  qrthoclase,  olivine,  and  hornblende. 
Silica  and  gr.  as  above. 

It  was   named  first  in   the  Vosges.     It   also   occurs  in 


PRIMARY  ROCKS.  1/5 

Saxony,  Bohemia,  France,  Jersey,  Great  Britain,  and  Scan- 
dinavia. The  orthoclase  is  flesh-red ;  mica  brown  to  black 
—seldom  green  ;  hornblende  grayish  to  dark  green.  On 
the  selvages  of  the  dikes  and  wherever  quickly  cooled  it 
becomes  compact.  The  folia  of  mica  are  sometimes  nearly 
half  an  inch  across;  the  feldspar  weathers  to  pinite  and 
kaolin  in  the  groundmass,  and  is  seldom  fresh.  Calcite 
and  siderite  are  also  secondary  products.  Chlorite  some- 
times occurs  ;  quartz  never. 

(a)  Hornblende-miuette,    with    predominant  hornblende, 
occurs  in  Alsace,  Erzgebirge,  the  Auvergne,  etc. 

(b)  Axgtte-minette,   with  predominant  augite,  occurs   in 
the  Vosges,  Fichtelgebirge,  Sweden,  England. 

(c)  Fraidronite  (E.  Dumas)  is  a  similar  rock,  much  weath- 
ered, from  France  in  a  limited  number  of  localities  (depart- 
ments of  the  Lozere,  Cevennes,  etc.).     It  is  of  dirty  green 
color,  with   weathered    felsitic  mass  carrying  much   mica, 
with  pyrite  and  quartz  as  secondary  products ;  also  calcite 
and  siderite  in  veins  and  included  balls.     The  rock  is  highly 
fissile  when   weathered.     The   above    rocks  are   variations 
between  mica-syenite  and  mica-syenite-porphyry. 

II.  VOSGESITE  (Rosenbusch). 

In  a  grayish-brown,  greenish-gray  to  black  groundmass 
of  similar  structure  to  minette,  composed  of  abundant 
and  generally  (ni)  orthoclase  and  other  syenitic  ingre- 
dients ;  but  showing  phenocrysts  of  only  hornblende 
and  augite.  A  quartz-free  syenite-porphyry  with 
predominant  hornblende  and  augite. 
Silica  48  ;  Gr.  2.93. 

It  occurs  in  narrow  dikes  in  the  Vosges,  Erzgebirge,  in 
Brazil,  and  (augite-vosgesite)  at  Livermore  Falls,  N.  H.  The 
rock  weathers  like  the  syenites  to  a  reddish  or  rusty  brown 
color,  and  is  the  parallel  of  minette,  with  biotite  replaced  by 
the  other  two  black  bisilicates.  These  are  so  predominant 


MANUAL    OF  LITHOLOGY. 

in  certain  localities  that  Rosenbusch  has  divided  the  rock 
into  amphibole-  and  augite-vosgesite.  The  former  bears  to 
the  hornblende-syenite-porphyry  and  hornblende-syenite  the 
same  relation  that  the  latter  does  to  the  augite  varieties  of 
the  rock.  In  both  plagioclase  appears  with  orthoclase ; 
hornblende  is  in  thin  and  augite  in  stout  prisms.  Uralite 
sometimes  appears.  Orthoclase  and  biotite  seldom  appear 
as  phenocrysts.  The  orthoclase  is  rich  in  soda.  This  rock 
is  decidedly  more  like  "  trap  "  than  minette,  from  its  color 
and  higher  gr.  Holocrystalline  and  porphyritic  textures 
occur  in  the  same  dike. 

GROUP  8.     DIORITIC    MICA-TRAP. 

II.  DIORITIC  MICA-TRAP,  Dioritic  Lamprophyre 

(Rosenbusch). 

A  series  of  dioritic  compounds  too  decidedly  porphyritic 
to  be  classed  as  typical  diorites,  and  too  granular  to  be 
placed  with  the  diorite-porphyrites.  Their  peculiar  texture 
is  observed  in  dike-rocks  and  masses  that  have  cooled 
against  moderately  hot  walls.  Their  hornblende  is  usually 
basaltic  and  rod-shaped,  their  magnetite  content  is  good, 
and  they  may  have  abundant  augite.  Rosenbusch  has 
distinguished : 

1.  Kersantite,  which  is  intermediate  in  texture  between 
mica-diorite  and  mica-porphyrite. 

2.  Camptonite,  which  is  intermediate  between  the  horn- 
blende varieties  of  the  same,  but  both  Zirkel  and  M.-Levy 
have  relegated  the  latter  back  to  diorite,  as  there  is  no  good 
reason  for  its  separation.     This  leaves  kersantite   and  its 
varieties  where  v.  Cotta  placed  them. 


PRIMARY  ROCKS. 

I.  KERSANTITE  (Delesse). 

A  porphyritic  rock,  rarely  so  fine-grained  as  not  to  be 
resolved  by  the  lens,  with  a  principal  mass  composed 
of  oligoclase  (or  oligoclase  and  biotite)  and  ortho- 
clase  (and  sometimes  sanidine),  and  carrying  pheno- 
crysts  of  oligoclase,  laminae  of  biotite,  fibers  of  horn- 
biende,  green  augite,  and  some  quartz,  olivine,  and 
magnetite. 

Silica  49-57 ;  Gr.  2.62-2.86. 

It  occurs  in  narrow  dikes,  which  sometimes  are  like  sur- 
face sheets,  in  Silesia,  Thuringian  Forest,  Alsace,  Austria, 
Bretagne,  and  Great  Britain.  The  rock  is  holocrystalline 
without  base.  The  oligoclase  phenocrysts  are  striped 
brown,  green,  red,  etc.,  from  decomposition  products.  They 
vary  from  rod  shapes  in  the  fine-grained  states  to  stout  ones 
in  those  of  coarser  grain  (in  some  cases  over  an  inch  long). 
Biotite  (or  anomite)  laminae  are  sometimes  nearly  half  an 
inch  across,  and  the  mineral  is  abundant  in  the  principal 
mass  as  in  minette,  and  on  the  selvages  it  is  parallel  to  the 
dike-walls.  Pyroxene  is  usually  green  augite,  also  enstatite 
and  bronzite,  which  latter  alter  to  bastite.  Hornblende  is 
the  brown  basaltic  kind,  rod-shaped  and  sometimes  £  inch 
long;  uralite  is  rare.  Quartz  occurs  as  in  granite,  and 
sometimes  forms  micropegmatite  with  orthoclase.  Now 
and  then  it  is  an  inch  across.  Quartz,  orthoclase,  and  oligo- 
clase also  occur  as  secondary  minerals,  with  calcite  and 
(rarely)  epidote  as  alteration  products.  Pyrite,  pyrrhotite 
and  garnet  also  occur.  In  some  localities  are  lenticular 
concretions  of  mica,  also  of  chlorite,  quartz,  and  reddish 
calcite. 

(a)  Kersanton  (Riviere).  A  rock  which  the  microscope 
has  shown  to  be  kersantite,  so  that  the  name  is  now  aban- 
doned. 


178  MANUAL   OF  LITHOLOGY. 

(b)  Aschaffite.     Some  authorities  place  this  rock  here. 
(See  under  "  Granite-porphyry.") 

(c)  6>/zW;^-kersantite    (Rosenbusch).     Here   olivine   is 
abundant    enough    to    attract    attention.      From    lower 
Austria. 

(d)  gtftfrte-kersantite  (Barrois).     In  small  massives  and 
a  dike  in  Spain.     A  bluish  green  dense  groundmass  (also 
fine-grained)  carrying  large  phenocrysts  of   plagioclase, 
biotite,  and  quartz.     Seldom  granitoid  or  wholly  dense. 
Secondary  calcite,  chlorite,  epidote,  and  muscovite  occur. 

(e)  /V/zte-kersantite  (Becke).     Poor  in  mica  and  rich  in 
augite,  the  former  having  chloritized.    Of  rare  occurrence. 


GROUP   9.      PORPHYRITE   AND   MICA-PORPHYRITE, 

lib.  ALKALI-LIME-SODA   SECTION. 

(Necessary  minerals,  plagioclase,  mica.) 

I.  PORPHYRITE,  Plagioclase-porphyrite. 

A  rock  with  a  compact  matrix  of  plagioclase  and  carry- 
ing phenocrysts  of  feldspars,  with  few  or  no  pheno- 
crysts of  the  black  bisilicates ;  occasionally  of  quartz. 
Silica  59-68  ,  Gr.  2.6-2.7. 

II.  MICA-PORPHYRITE. 

A  similar  rock  carrying  abundant  phenocrysts  of  mica, 
and  also  of  feldspar,  hornblende,  and  infrequently  of 
pyroxene. 

Silica  60-67;  Gr.  2.6-27. 

Kporphyrite,  in  distinction  from  a  porphyry,  is  a  rock  with 
a  matrix  of  plagioclase  rather  than  of  orthoclase.  Both 
rocks  contain  both  feldspars ;  but  in  the  porphyry  the  alkali 
form  predominates  and  the  quartz  content  is  high :  in  the 
porphyrite  the  Ca-Na-form  predominates  and  quartz  is 


PRIMARY  ROCKS.  1 79 

rare  (either  in  the  groundmass  or  as  phenocryst).  The  old 
distinction  between  the  two  rocks  on  the  score  of  the  pres- 
ence or  absence  of  quartz  as  phenocryst  or  in  the  mass  is 
no  longer  held.  As  the  phenocrysts  are  predominant 
plagioclase,  mica,  hornblende,  or  pyroxene,  the  porphyrite 
is  called  plagioclase-,  mica-,  hornblende-,  or  pyroxene-por- 
phyrite.  Zirkel  classes  all  except  the  pyroxene  varieties 
under  "  diorite-porphyrite."  The  first  two  types  (plagio- 
clase and  mica)  will  be  treated  here.  The  groundmass 
varies  alike  in  both,  and  the  phenocrysts  are  similar.  After 
a  general  description  they  will  be  further  noted  apart. 
They  occur  mostly  in  thin  dikes ;  intrusive  sheets ;  as  bosses 
and  in  tuffs.  They  are  also  frequently  found  as  old  extru- 
sive sheets  of  great  thickness,  so  that  they  partake  of  both 
extrusive  and  intrusive  characters.  They  therefore  show 
stretched  vesicular  structures,  both  empty  and  filled  with 
green  earth  and  calcite,  which  frequently  form  the  greater 
part  of  the  mass.  The  masses  are  irregularly  jointed  and 
fissured  ;  rarely  columnar  and  tabular.  They  are  less  wide- 
spread than  the  quartz-porphyries,  and  do  not  form  such 
large  masses.  They  are  found  in  Saxony,  the  Harz,  Black 
Forest,  Vosges ;  in  Belgium,  Bohemia,  Tyrol,  Italy,  Monte- 
negro, Spain,  Asia,  Africa ;  in  the  Augusta  Mountains, 
Nev. ;  New  Hampshire,  Vermont,  New  York,  and  Canada. 
The  porphyrites  will  be  separated  from  melaphyre  by  the 
olivine  content  of  the  latter;  so  that  both  are  plagioclase- 
porphyries  (using  the  term  in  its  general  meaning) ;  porphy- 
rite being  without,  and  melaphyre  with,  olivine.  As  in  all 
mixtures  there  are  points  where  several  minerals  seem  to 
be  equally  predominant,  and  where  the  rock  is  a  transition 
between  two  types.  There  is  also  the  point  where  the  black 
bisilicates  retreat  into  the  groundmass  and  only  plagio- 
clase shows.  Here  the  microscope  must  decide  as  to  the 
variety,  unless  either  quartz  or  orthoclase  appear,  and  then 


180  MANUAL    OF  LITHOLOGY. 

it  will  belong  to  the  micaless  porphyrites.  All  types  of 
porphyrite  with  no  (or  few)  phenocrysts  of  black  bisilicates 
will  be  grouped  under  porphyrite.  Three  types  of  ground- 
mass  are  given  for  the  purpose  of  making  clear  some  of  the 
following  divisions,  though  the  types  can  only  be  dis- 
tinguished (m). 

(a)  Greenstone-like   porphyrite.     With  a  (m)  crystalline 
groundmass   like    diorite,   green  through  chloritization    or 
formation  of  epidote  from  hornblende  ;  greenish  hornblende, 
also  green  by  transmitted  light ;  dirty  greenish  white  feld- 
spar; biotite  not  very  dark;  little  or  no  base.     It  forms  as 
a  rule  bosses  from  which  dikes  run  into  the  older  schists, 
and  makes  what  may  be  extrusive  as  well  as  intrusive  sheets. 
Most  of  the  hornblende-  and  mica-porphyrite  dikes  in  cen- 
tral Tyrol,    beds  in  the  Alps,  dikes  in  the  Falkenstein,  in 
Sweden,  Belgium,  etc.,  are  examples  of  this  type. 

(b)  Andesitic-porphyrite.     (m)  like   andesite,  with  gray, 
grayish  black,  brownish  black  color ;  fresh  and  almost  glassy 
plagioclase ;  hornblende  brownish  black  and  brown  in  sec- 
tion;  biotite  very  dark;  not  much  quartz;  groundmass  rich 
in  ferrite  and  with  andesitic  structure,  sparingly  microdio- 
ritic;  with  small  amount  of  glass  base  (colorless,  yellowish, 
grayish).     Found  in  the  Thuringian  Forest,  Saar-Nahe  dis- 
trict, etc.,  as  dikes. 

(c)  Porphyry-like  Porphyrite.     (m)  like  the  porphyries 
and   sometimes   micropegmatitic   and    microfelsitic ;    color 
reddish,  brownish  red ;   or  chestnut-brown  (from  ferrite) ; 
poor  in  black  bisilicates ;  richer  in  silica  than  (b] ;  quartz 
quite  abundant  as  (M)  phenocrysts  and  in  the  groundmass ; 
in  many  cases  the  groundmass  is  (m)  compact.     In  Alsace, 
Silesia,  Altai  Mountains,  Saar-Nahe  district,  as  dikes. 

Plagioclase  phenocrysts  are  white,  yellowish  white,  or 
reddish  white,  and  usually  somewhat  altered  and  dull. 
They  are  oligoclase,  sometimes  andesine,  less  frequently 


PRIMARY  ROCKS.  l8l 

labradorite.  When  hornblende  is  present  it  is  as  stout 
prisms  or  acicular  shapes  of  brownish  black  color.  Biotite 
occurs  in  regular  hexagonal  tables,  sometimes  in  prisms, 
rarely  in  folia.  Quartz  occasionally  appears  in  large  phen- 
ocrysts,  as  do  orthoclase  and  garnet.  Augite  is  now  and 
then  (M). 

I.  PLAGIOCLASE-PORPHYRITE,  Porphyrite. 
In  a  groundmass  with  a  habit  like  that  described  in  (c) 

are  phenocrysts  of  plagioclase  (usually  oligoclase,  fre- 
quently andesine,  less  so  labradorite),  and  sometimes 
orthoclase  and  quartz. 

Silica  60-68  ;  Gr.  2.6-2.7. 

It  occurs  in  the  Black  Forest,  Bohemia,  Scotland,  Altai 
Mountains,  Ecuador.  The  groundmass  is  gray,  red,  violet, 
or  blue,  in  which  the  phenocrysts  are  well  contrasted.  In 
the  Rothliegenden  formation  of  Germany  it  is  found  in  a 
thick  extrusive  sheet. 

II.  MICA-PORPHYRITE. 

A  groundmass  as  above,  with  predominant  phenocrysts 
of  biotite  and  plagioclase,  also  orthoclase  and  quartz. 
Silica  60-67  ;  Gr.  2.5-2.8. 

This  is  found  in  Saxony,  the  Thuringian  Forest,  Saar- 
Nahe  district,  central  Alps,  etc.  Kemp  reports  an  augite- 
mica-porphyrite  in  bosses  west  of  Deckertown,  N.  J. 

I.  Quartz-mica-porphyrite. 

A  porphyrite  with  light  green  tabular  plagioclase  pheno- 
crysts ;  dark  biotite  tables  (more  frequently  in  folia  than  in 
the  quartzless  varieties) ;  rounded  grains  of  quartz  and 
sometimes  double  pyramids ;  frequently  orthoclase  f  inch 
long.  The  groundmass  is  a  (m)  aggregate  of  angular  quartz 
and  feldspar  prisms.  Silica  62-78  ;  Gr.  2.74. 


S  82  MANUAL    OF  LITHOLOGY. 

It  occurs  in  dikes  and  is  found  in  Alsace,  Austria,  the 
Alps,  etc.,  and  from'Gippsland,  Australia,  a  variety  with 
the  high  silica  content  of  72-77.66  is  reported. 

(a)  Malchite  (Osann),  from  the  Melibocus,  as  a  dike- 
rock  of  the  diorite  group,  with  silica,  63.18.  The  dense 
groundmass  carries  rare  phenocrysts  of  dark  biotite,  pale 
green  labradorite,  and  quartz ;  with  (m)  green  hornblende, 
.sphene,  and  allanite. 

INTERMEDIATE  DIVISION— LIME-SODA  SECTION. 
GROUP   10.     DACITE. 

Ilia.    DACITE  QUARTZ-DIORITE  EXTRUSIVES. 
(Necessary  minerals:   Plagioclase,  hornblende,  and  quartz.) 

DACITE  (Stache),  Quartz-hornblende-andesite. 
Named  from  the  old  Roman  province  of  Dacia,  where  it 
was  first  found.  The  rock  will  be  considered  as  always 
showing  free  quartz  either  (M)  or  (m),  though  Zirkel  classes 
all  rocks  of  similar  mineral  content  with  the  average  of  silica 
of  the  quartzose  varieties  as  dacite,  whether  they  show  free 
quartz  or  not.  On  the  other  hand,  Rosenbusch  includes 
quartzose  augite-andesites.  As  Lang  has  shown  that  bulk 
analyses  are  of  no  value,  and  as  the  original  rock  was  required 
to  show  free  quartz,  it  will  be  so  considered. 
This  group  comprises : 

I.  Dacite. 
II.  Mica-dacite. 

III.  Pantellerite. 

IV.  Dacite  glass. 

V.  Pantellerite  glass. 


PRIMARY  ROCKS.  183 

I.  DACITE  (Stache). 

A  somewhat  lighter-colored  groundmass   than  that   of 
hornblende-andesite,  which  shows  large  phenocrysts 
of  glassy  (sanidine-like)  plagioclase,  much  hornblende, 
biotite,  quartz,  and  sometimes  sanidine. 
Silica  62-72  ;  Gr.  2.5-2.6. 

It  occurs  as  surface  sheets  and  lava-streams,  as  dome- 
•shaped  hills,  and  as  dikes,  associated  with  hornblende-ande- 
site. It  is  found  in  Germany,  Hungary,  Iceland,  Armenia, 
Japan,  Mexico,  South  America,  New  Zealand,  and  abun- 
dantly in  the  western  United  States  in  the  Great  Basin. 
The  rhyolitic  variety  of  groundmass  is  distinguished  from 
that  of  rhyolite  with  great  difficulty,  as  the  plagioclases 
have  (even  (m) )  the  habit  of  sanidine,  and  only  the  greater 
silica  content  can  settle  the  question.  This  is  the  case  with 
the  American  dacites  (Zirkel).  The  plagioclase  is  usually 
andesine  ;  oligoclase,  labradorite,  and  anorthite  follow  in 
decreasing  importance.  Quartz  is  (M)  in  round  grains  and 
in  sharp-angled  double  pyramids  (f  inch  long  in  Java),  be- 
tween dark  and  bluish  gray,  in  some  cases  yellow  or  rose- 
red.  In  many  varieties  the  quartz  is  only  as  phenocrysts. 
Hornblende  and  biotite  often  replace  one  another.  The 
former  is  usually  brown  and  alters  to  viridite  and  calcite. 
In  some  intances  biotite  alone  appears.  Augite  is  not  abun- 
dant either  (M)  or  (m).  The  (M)  accessories  are  zircon, 
orthite,  cordierite,  and  red  garnet.  Olivine  is  usually  ab- 
sent. An  increase  in  sanidine  makes  this  a  trachyte,  and  a 
failing  in  quartz  (or  in  the  silica  content)  a  hornblende-ande- 
site. 

(a)  Timazite  (in  part).  The  more  acid  varieties  of  tima- 
zite  (plagioclase,  gamsigradite,  mica,  magnetite,  and  quartz) 
with  silica  67.4  belong  here.  It  is  also  found  in  the  Vosges. 


184  MANUAL   OF  LITHOLOGY. 

II.  QUARTZ  MICA-ANDESITE,  Mica-Dacite. 
This  bears  to  dacite  the  same  relation  that  mica-andesite 

does  to  hornblende-andesite. 

III.  PANTELLERITE  (Foerster). 
Rosenbusch  calls  this  a  transition  between  the  "  dacites  " 

(using  the  term  for  all  quartz-andesites)  and  the  rhyolites, 
from  its  high  silica  content.  It  forms  extensive  lava-streams 
in  the  island  of  Pantelleria,  which  have  at  times  a  trachytic 
and  a  rhyolitic  facies,  with  a  third  which  is  a  mean  between 
them.  The  groundmass  is  rich  in  iron  and  carries  pheno- 
crysts  of  plagioclase,  anorthoclase,  triclinic  amphibole 
(cossyrite),  aegirite-like  augite,  and  no  quartz,  tridymite,  or 
biotite.  The  "  trachytic  "  groundmass  has  a  web  of  feld- 
spars and  augite  needles.  The  "rhyolitic"  groundmass 
has  considerable  glass  base  and  carries  the  same  minerals. 
It  contains  silica  66.8-72.5  ;  Gr.  2.6.  Some  authorities  style 
it  a  pitchstone-porphyry  with  a  granular  groundmass. 

(a)  Volcanite  (Hobbs).  From  Volcano,  Italy,  in  bombs. 
A  rock  with  glass  base  and  groundmass  of  anorthoclase, 
andesine,  acmite,  and  olivine,  carrying  phenocrysts  of  the 
minerals,  and  with  silica  66.99.  In  structure  and  composi- 
tion this  is  an  augite-pantellerite. 

IV.  DACITE  GLASS. 

This  weathers  by  changes  occurring  along  the  perlitic 
cracks,  and  working  inward  till  the  whole  mass  is  white  and 
opaque,  and  soft  enough  to  be  scratched  by  the  finger-nail. 
When  put  into  cold  water  it  breaks  into  small  fragments 
which  fall  to  powder.  By  levigating  this  the  unweathered 
feldspar  phenocrysts  can  be  secured  intact. 

(a)  Dacite-felsite.  Although  this  is  not  a  glass,  it  is  prob- 
ably a  devitrified  one,  and  runs  readily  into  perlite.  It 
occurs  at  Arran,  Scotland. 


PRIMARY  ROCKS.  1 8$ 

i.  Blue  Porphyry.  At  Mt.  Esterel,  department  of  Var, 
France.  Silica  69.  A  (m)  microfelsitic  mass  carrying  pheno- 
crysts  of  andesine  (3  mm.),  abundant  sanidine,  and  acicular 
hornblende.  Zirkel  puts  this  as  rhyolite  from  its  high  acid- 
ity, but  chemical  analyses  are  uncertain  guides,  and  some 
dacites  have  been  reported  with  still  higher  silica  content. 

(b)  Dacite-pitchstone-porphyry.     From  Arran.    .A  black 
rock  readily   breaking  into  spheroids  when  struck  with  a 
hammer.     These  are  momentarily  bright,  but  immediately 
cloud  with  a  whitish  film,  which  is  considered  to  be  caused 
by  relief  from  strain  and  corresponding  molecular  change. 

(c)  Perlitic    Dacite.      From    Mitake,   Japan  ;    Colombia, 
Ecuador.     A  dacite  glass  carrying  (m)  phenocrysts  and  per- 
litic   globules — some   3   mm.     In  one  case  the  dacite  lava- 
stream  had  a  layer  of  perlite  crusted  with  pumice. 

(d)  Dacite-obsidian.     Is  reported  in  Hungary,  Cabo  de 
Gata,  Ecuador,  Italy. 

(e)  Perlitic   Dacite-pumice.      Containing  spherules  and 
phenocrysts,  from  northwestern  South  America. 

(f)  Dacite-pumice.    From  the  west  coast  of  South  Amer- 
ica.   In  some  cases  the  phenocrysts  are  quite  large.    Quartz 
is  1-3  mm. 

V.  PANTELLERITE  GLASS. 

A  third  variety  of  pantellerite  (see  p.  184)  is  a  highly 
glassy  base  with  a  few  microliths  of  augite  and  cossyrite,  and 
carrying  phenocrysts  of  plagioclase,  augite,  and  cossyrite. 

A  fourth  variety  comprises  the  following  states:  obsid- 
ian, obsidian-porphyry,  porphyritic  pumice,  pumice. 


1 86  MANUAL    OF  LITHOLOGY. 


GROUP    n.     QUARTZ-DIORITE. 

Ilia.  DACITE-QUARTZ-DIORITE  INTRUSIVES. 
(Necessary  minerals  :  Plagioclase,  hornblende,  and  quartz.) 

QUARTZ-DIORITE. 

A  diorite  carrying  either  (m)  or  (M)  free  quartz.  This 
can  be  divided  into  : 

I.  Quart  z-hornblende-<Mor\te. 
II.  Quart  z-mica-di\or\te. 

III.  Quart 'z-frornlt/ende-porphyrite. 

IV.  Q2iartZ'mica-hornblende-pQYp\iyrite. 
V.  Diorite-glass, 

I.  QUARTZ-HORNBLENDE-diorite. 
A  coarse-  to  fine-grained  crystalline-granular  compound 
of  Ca-Na-feldspar  (frequently  (m)  orthoclase),  horn- 
blende, grayish-white  quartz,  and  the  other  minerals 
.  more  fully  given  under  diorite ;  of  dark-blue,  blackish 
green,  sometimes  light-brown  color.  The  minerals 
are  as  given  under  diorite  (q.  v.\  except  that  quartz  is 
always  present.  It  occurs  in  rounded  and  angular 
grains,  generally  (M),  rarely  in  double  pyramids  in 
the  granular  states. 

Silica  55-67;  Gr.  2.6-2.9. 

It  occurs  like  diorite,  and  is  found  with  it,  and  especially 
in  the  Black  Forest,  the  Vosges,  the  Odenwald,  Servia, 
Bohemia,  France,  Belgium,  Scotland,  Hungary,  Spain, 
Portugal,  and  at  Cortlandt,  N.  Y.  In  the  Andes  quartz  6-8 
mm.  occurs.  V.  Cotta's  banatite  is  a  quartz-diorite  in  part, 
and  part  diorite,  with  andesine.  The  anorthite-diorite  of 
Corsica  has  quartzose  varieties.  Orthoclase  and  quartz 
form  micropegmatitic  textures. 


PRIMARY  ROCKS.  l8/ 

II.  QUARTZ-MICA-diorite,  Tonalite  (vom  Rath). 
A     fine-crystalline-granular     compound     of     oligoclase, 

orthoclase,    quartz,    blackish-green    hornblende,    and 
brown  mica. 

Silica  66-70  ;  Gr.  2.7-2.9. 

It  forms  the  principal  mass  of  the  Adamello  Mountains 
In  southern  Tyrol  and  is  named  from  the  Tonale  Pass.  It 
also  occurs  in  France,  Saxony,  Mexico,  Australia,  Japan, 
St.  John,  N.  B.,  and  in  the  Highlands  of  Scotland  it 
grades  on  the  one  hand  into  quartz-diorite,  and  on  the  other 
into  hornblende  granitite.  Oligoclase  is  snow-white  and 
-contains  but  57  per  cent  of  silica  ;  quartz  is  one-third  of 
the  mass  in  grayish  grains  ;  hornblende  and  mica  are  in 
small  amounts — the  hornblende  in  stout  prisms  (sometimes 
one  foot  long),  and  the  mica  in  irregular  folia.  As  acces- 
sories are  orthoclase  (which  forms  pegmatite  (m)  with 
quartz),  zircon,  garnet  (an  inch  in  diameter),  sphene,  titanite, 
magnetite,  pyrite,  and  corundum.  It  was  once  called  a 
.granite.  In  some  specimens  primary  concretions  occur  of 
dark  mica  and  hornblende,  with  but  little  feldspar  and  no 
-quartz,  and  the  Japanese  rock  abounds  in  acicular  tourma- 
line. Garnet  is  common. 

III.  QUARTZ-HORNBLENDE-porphyrite. 

For  the  varieties  of  groundmass  in  diorite-porphyrite  see 
p.  179,  as  well  as  for  the  predominant  minerals.  The 
presence  of  quartz  phenocrysts  is  necessary  to  form 
this  variety. 

Silica  50-65;  Gr.  2.6-2.7. 

(a)  Black  Porphyry.  From  near  Lugano,  Italy.  A  light- 
gray  to  dark-green  or  dark-red  groundmass  with  predomi- 
nant feldspars,  chloritized  hornblende  prisms,  sporadic  mica 
folia,  and  quartz. 


1 88  MANUAL    OF  LITHOLOGY. 

(b)  Amygdalophyre  (Jenzsch).  From  near  Dresden  as  sheets 
and  tuffs.     The  groundmass  is  greenish  brown  and  some- 
what transparent  on  thin   margins.      As   phenocrysts   are 
feldspar    and    hornblende.      The   former    is    altered,    the 
groundmass  chloritized,  but  shows  brownish  glass  in  fresh 
specimens.     On  the  hanging-wall  side  are  amygdules  filled 
with    hornstone,  chalcedony,  quartz,  chlorophasite,  pyrite, 
and  galenite. 

(c)  Bergamaskite.     From  Bergamo.    Carries  arfvedsonite. 

(d)  Diorite-quartzifera-porfiroide  (Alfonso    Cossa).     From 
Cossato.     Shows  a  grayish  (m)  crystalline  groundmass  with 
green  and  brown  hornblende  and  quartz. 

IV.  QUARTZ-MICA-hornblende-porphyrite. 
(a)  Paleophyre  (Giimbel).  A  dike  in  the  Silurian  of  the 
Fichtelgebirge.  A  fine-grained  reddish  groundmass  with 
well-crystallized  phenocrysts  of  oligoclase,  brown  horn- 
blende, brown  biotite,  and  corroded  quartz.  Hornblende 
and  biotite  are  strongly  chloritized,  and  the  groundmass  is 
full  of  ferrite  and  calcite.  It  is  an  aggregate  of  (m)  feldspar 
without  any  of  the  black  bisilicates. 

V.  DIORITE  GLASS 

As  the  vitreous  states  of  a  rock  are  found  to  be  more 
siliceous  than  the  crystalline  ones,  the  diorite  glasses  will  be 
placed  here.  They  are  rare,  but  are  found  with  all  sorts  of 
diorite  eruptions,  and  are  due  to  the  rate  of  cooling  rather 
than  to  the  chemical  composition.  Following  the  analogy 
of  other  rocks,  it  may  be  permitted  to  say  that  the  more 
acid  diorites  would  be  more  ready  to  show  glassy  states  on 
sudden  cooling  than  the  more  basic,  and  to  a  greater  extent. 

1.  Diorite  -  mica -pitchstone- porphyry.  With  conchoidal 
fracture  ;  black ;  carrying  phenocrysts  of  small  rust-colored 
feldspars  (mostly  plagioclase),  much  mica  in  folia,  few 


PRIMARY  ROCKS.  189 

grayish  quartz  grains.  The  base  is  light  brown,  dark-gray 
to  black,  and  shows  flow  structure.  Hornblende  is  scanty. 
Silica  62.02 ;  Gr.  2.466.  It  is  found  in  Italy  and  Scotland. 

2.  TdioicitQ-inica-hornblende-pitchstone-porphyry.      From  the 
southern  Tyrol,  with  mica  and  hornblende  abundant  (also 
enstatite),  and  with  microfelsitic  (m)  base. 

3.  Pitchstone-peperite  (v.  Lasaulx).    From  Monte  Trisa.    A 
vesicular   glass    that    changes   to   compact   and    granular 
states,  with  abundant    (and  often  chloritized)   hornblende, 
small   feldspars    (usually   plagioclase),    folia   of   mica,   and 
pyroclasts    of   country-rock.      It  is   amygdaloidal   from   a 
chalcedonic  filling  of  vesicles. 

(A  full  discussion  of  the  various  lorms  of  occurrence, 
the  states,  textures,  structures,  minerals,  as  well  as  a 
definition  of  the  porphyrites,  will  be  found  in  its  proper 
place  under  "  Diorite,"  as  these  quartzose  forms  are  infre- 
quent, of  small  extent,  and  are  but  appendages  to  the  large 
group  of  the  diorites.) 

GROUP  12.     ANDESITE. 

I  lib.   HORNBLENDE-ANDESITE-DIORITE  EXTRUSIVES. 
(Necessary  minerals:  Ca-Na-feldspar  and  hornblende.) 

ANDESITE  (L.  v.  Buch). 

A  group  of  extrusives,  generally  dark-colored,  with  a 
restricted  amount  of  glass  base,  but  larger  than  in 
trachyte,  and  carrying  a  similar  (m)  web  of  minute 
crystals,  plagioclase,  hornblende,  biotite,  and  pyrox- 
ene, either  monoclinic  (augite  or  diallage)  or  rhombic 
(enstatite  or  hypersthene),  and  with  or  without 
quartz.  In  this  groundmass  plagioclase  and  some,  or 
all,  of  the  above  appear  as  phenocrysts. 

These  rocks  were  first  studied  in  the  Andes,  whence  the 
name,  and  in  them  was  found  a  feldspar  that  was  first  called 


MANUAL    OF  LITHOLOGY. 

albite,  then  oligoclase,  and  afterwards  (from  the  locality) 
andesine.  It  is  now  known  that  all  of  the  albite-anorthite 
series  are  present  (except  albite).  In  some  varieties  the 
prevalent  minerals  are  andesine  and  labradorite,  with  oligo- 
clase frequently,  and  rarely  bytownite  or  anorthite.  These 
carry,  as  a  r^le,  hornblende  and  more  or  less  black  mica. 
In  other  varieties  the  feldspars  belong  to  the  andesine- 
anorthite  end  o\  the  series,  and  carry  the  pyroxenes  as 
necessary  minerals.  There  is  thus  a  more  acid  and  a  more 
basic  division,  which  were  called  by  J.  Roth  hornblende- 
andesite  and  augite-andesite.  The  latter  is  distinguished  from 
basalt  by  its  texture,  and  the  much  smaller  amount  of 
olivine.  These  were  first  classed  with  the  trachytes,  but 
were  distinguished  by  the  absence  of  alkali  feldspars.  There 
are  certain  rocks,  however  (to  be  described),  which  are 
transitions  between  these  effusive  groups,  as  they  carry  both 
feldspars.  The  group  will  be  divided  as  follows : 

I.  Hornblende-andesite.     Plagioclase  and  hornblende. 

la.  Mica-andesite.  Plagioclase  and  biotite  (always  some 
hornblende). 

The  andesites  are  effusive  equivalents  of  abyssal  diorite,, 
and  Judd  reports  that  in  the  island  of  Mull  there  exist 
laccoliths  that  can  be  traced  from  diorite  to  andesite. 


PRIMARY  ROCKS.  IQI 

I.    HORNBLENDE -ANDESITE     (Roth),     Gray 

Trachyte  (v.  Richthofen). 

A  (m)  fine-grained  to  compact  (sometimes  coarse  gran- 
ular) groundmass  of  light  or  dark  color  (usually  gray- 
ish or  brownish  black)  and  waxy,  greasy  luster,  which 
'(m)  shows  a  moderate  amount  of  glass  base  filled  with 
a  matt  of  minute  feldspars,  magnetite  grains,  horn- 
blende, augite,  and  (sparingly)  biotite,  and  carrying 
(M)  phenocrysts  of  vitreous  plagioclase,  hornblende 
in  large  black  prisms  and  needles,  and  some  augite. 
As  accessories  appear  (M)  magnetite,  apatite,  quartz, 
tridymite,  haiiyne,  garnet,  and  sometimes  olivine,, 
and  (m)  an  abundance  of  cordierite,  zircon,  and 
(rarely)  titanite. 

Silica  55-62 ;  Gr.  2.6-2.8. 

It  ocgurs  in  isolated  peaks  and  dome-shaped  masses  (as 
in  Germany,  Scotland,  etc.),  in  laccoliths ;  is  common  in 
lava-streams  (as  in  the  Andes),  sometimes  as  surface  sheets,, 
rarely  in  dikes.  It  is  found  in  the  Siebengebirge,  Eifel, 
Westerwald,  Hebrides,  central  France,  Hungary,  Bosnia,, 
the  Canaries  and  Azores,  East  Indies,  Japan,  Australia, 
South  and  Central  America,  Nevada,  California,  Oregon. 
The  (M)  structure  of  quartzless  hornblende-  and  mica-ande- 
sites  varies  greatly.  The  shades  may  be  light  or  dark;  as  a 
rule,  they  are  gray  or  brown,  also  bluish,  reddish,  red,  bluish 
red,  and  reddish  purple,  and  the  reddening  is  due  to  the 
oxidation  of  the  iron  in  the  black  bisilicates  (usuaHy  augite). 
The  groundmass  is  sometimes  compact,  as  in  augite-andesite, 
but  usually  rough  and  porous,  as  in  trachyte;  (M)  fluidal 
structures  are  uncommon.  In  some  localities  the  laminae  of 
mica  are  parallel.  The  phenocrysts  are  usually  plagioclase, 
with  either  hornblende  or  mica,  or  both,  and  sometimes 
sanidine.  When  both  feldspars  are  present,  the  variety  is 
intermediate  with  trachyte.  The  plagioclase  is  generally  in 


I92  MANUAL    OF  LITHOLOGY. 

regular  crystals,  sometimes  tabular,  and  rarely  irregular.  It 
is  usually  andesine  or  labradorite,  sometimes  an  oligoclase 
near  andesine  in  composition  (crystals  sometimes  over  two 
inches  in  length),  and  sometimes  one  of  the  basic  plagio- 
clases,  but  rarely  as  basic  as  anorthite.  Hornblende  is 
in  large  black  prisms  and  needles  which  are  frequently 
several  inches  long ;  brown  by  transmitted  light,  but  green 
when  altered  (to  epidote,  ferrite,  or  opal).  In  some  cases  the 
(M)  phenocrysts  disappear  and  hornblende  is  found  only  in 
the  groundmass  and  (M).  Biotite  is  in  large  hexagonal 
folia,  brownish  to  blood-red  by  transmitted  light.  It  rarely 
occurs  in  the  groundmass,  but  exists  as  phenocrysts  (M) 
and  (m),  and  seldom  without  hornblende.  Augite  is  abundant 
in  the  groundmass  and  as  (M)  phenocrysts  (which  are  some- 
times f. inch  long)  in  both  hornblende- and  mica-andesites, 
and  is  rarely  absent.  Delessite  is  also  reported  from  Italy. 
Rhombic  pyroxene  is  found  in  such  amounts  as*  to  form 
hypersthenic  varieties.  In  such  cases  it  is  also  found  in  the 
groundmass.  Of  the  accessories,  quartz  appears  in  reddish 
grains,  and  an  abundance  of  it  changes  the  rock  to  dacite. 
Tridymite  is  sometimes  1.5  mm.  long,  but  it  generally  is  an 
uncertain  component.  Hauyne  is  in  blue  or  white  (from 
weathering)  grains,  and  is  essential  in  some  varieties.  Gar- 
net is  sometimes  half  an  inch  in  diameter.  Olivine  is  rare 
and  sporadic;  sometimes  4  mm.,  but  usually  (m).  The 
secondary  minerals  are  carbonates  of  lime  and  iron,  bastite, 
quartz,  opal,  chalcedony,  zeolites,  and  specular  iron.  Black- 
ish-blue concretions  are  sometimes  nearly  an  inch  in  diam- 
eter, and  are  composed  (m)  of  plagioclase  and  some  of  the 
black  bisilicates.  We  can  distinguish  : 

i.  Granitoid  Hornblende  -  ande site  (Miigge).  A  coarse- 
grained rock  from  S.  Miguel,  Azores,  with  neither  ground- 
mass  nor  glass  base,  but  consisting  of  equally  large  grains 
(M)  of  plagioclase,  hornblende,  biotite,  augite,  and  apatite. 


PRIMARY  ROCKS.  193 

A  similar  compound  of  plagioclase  and  hornblende  with  a 
small  amount  of  glass  and  apatite,  but  no  groundmass,  is  also 
reported. 

2.  Augite-free  Hornblende-andesite    (Hague).      From    the 
Eureka  district,  Nev.,  with  (m)  abundant  glass  inclusions, 
and  needles  of  apatite. 

3.  Hyper sthene-hornblende-andesite.     At  Lassen's  Peak  and 
Mount  Shasta,  CaL,  San  Salvador,  the  Siebengebirge,  South 
America,  and  elsewhere.     This  is  mostly  hypersthene,  with 
a  little  augite  (m)  in  the  groundmass,  with  phenocrysts  of 
the  same,  plagioclase,  hornblende,  and  mica. 

la.  MICA-ANDESITE,  Biotite-andesite. 

A  variety  of  the  above  where  biotite  is  predominant  over 
hornblende.  In  some  cases  the  latter  is  almost  absent  from 
the  groundmass.  The  rock  resembles  hornblende-andesite, 
and  has  similar  essentials  and  accessories.  The  groundmass 
weathers  to  opal.  Its  usual  colors  are  dark  gray,  red,  red- 
dish brown.  It  occurs  in  Greece,  Asia  Minor,  South 
America,  California. 

Under  this  general  subdivision  come  : 

1.  Isenite  (Bertels).     From  the  Sengelberg  in  the  Wester- 
watd,  which  was  wrongly  defined  till  Rosenbusch  found  a 
labradorite-bytownite-plagioclase,  hornblende,  much  light- 
green    augite   (in   the   groundmass),    irregular    light-green 
grains  of  olivine,  and  sporadic  biotite  and  apatite.     It  is 
named  from  a  small  stream  (Eis,  Latin  Isena)  in  the  neighbor- 
hood. 

2.  Timazite    (Breithaupt),    (in    part)    Trachytic   Green- 
stone.    From  Timok  valley  in  eastern  Servia.     A  gray  or 
greenish-gray  felsitic  groundmass  carrying  phenocrysts  of 
white  plagioclase,  velvet-black  hornblende  (gamsigradite), 
mica,    magnetite,    and   pyrite.      Silica    51.      A   more   acid 
variety  belongs  to  dacite  (q.  v.). 


194  MANUAL   OF  LITHOLOG  Y. 

3.  Trachydolerite  (Abich).  A  fine-grained  compound  of 
oligoclase  or  labradorite,  hornblende,  magnetite,  augite,  and 
sometimes  mica,  forming  a  gray  or  brown  groundmass,  and 
carrying  the  same  as  phenocrysts.  Silica  54-61$ ;  Gr. 
2.7-2.8.  This  is  an  intermediate,  as  its  name  implies.  It 
occurs  compact,  vesicular,  etc.,  at  the  Peak  of  Teneriffe,  in 
Kamtschatka,  Italy,  etc.  This  is  an  augitic  hornblende- 
andesite,  which  frequently  becomes  augite-andesite  by  in- 
crease in  augite  and  by  entrance  of  olivine,  as  at  Lowen- 
berg,  Siebengebirge  •  shades  into  dolerite.  It  is  no  longer 
known  as  a  separate  rock. 

HORNBLENDE-ANDESITE   GLASS. 

This  is  reported  as  yet  only  in  a  few  cases.  Zirkel 
states  that  it  is  not  found  in  Hungary  nor  the  Sieben- 
gebirge, where  there  occurs  the  greatest  development  of  the 
rock. 

(a)  Perlitic  Hornblende-andesite.       In  a  (m)   crystalline 
groundmass  occur  perlitic  spheres  of  glass.    From  Akerotivi, 
island  of  Thera.     At  Balos  the  spheres  can  be  separated 
from  the  matrix  when  it  is  fractured. 

(b)  Perlitic    Hornblende-andesite-pitchstone.      A    black 
pitchstone  with  great  spherules,  from  Muzukishima,  Japan, 
with  almost  (m)   biotite  and  garnet,  and  great  (M)  plagio- 
clases  as  phenocrysts. 

(c)  Perlitic  Hornblende-andesite-/&w^.    At  the  last  local- 
ity, and  the  Isle  of  Luzon.     The   pumice  is  a  white  glass 
with  dark-green   hornblende,  glassy  andesine,  and  biotite, 
among  which  are  distributed  the  glassy  spherules. 

(d)  Hornblende-andesite-/?/ mice.      At    Montserrat,    San 
Salvador,  and  Peru.     The  pumice  is  rose-red,  and  frequently 
has   the   vesicles   so   much   stretched   as   to  resemble  fine 
fibers  in  a  glassy  mass  that  carries  phenocrysts  of  the  com- 
ponent minerals. 


PRIMARY  ROCKS. 


GROUP  13.     DIORITE. 

f    IHb.  HORNBLENDE-DIORITE-ANDESITE  INTRUSIVES. 
(Necessary  minerals  :  Ca-Na-feldspar  and  hornblende.) 

DIORITE  (Hatty). 

A  holocrystalline,  usually  coarse-  to  fine-grained  com- 
pound of  a  Ca-Na-feldspar  and  hornblende,  with  mica 
and  pyroxene.     This   also   shbws    compact   and  vit- 
reous states  and  exhibits  phenocrysts. 
Silica  45-67  ;  Gr.  2.6-2.9. 

It  occurs  rarely  in  small  bosses,  but  mostly  as  dikes 
and  intrusive  sheets  ;  the  former  are  usually  fine-grained 
at  their  margins  and  coarsely  crystalline-granular  towards 
their  middle.  The  intrusive  sheets  are  sometimes  of 
considerable  extent,  and  follow  more  or  less  closely  the 
planes  of  stratification  of  the  rocks,  usually  crystalline 
schists,  gneiss,  etc.,  into  which  they  have  been  intruded. 
Dikes  of  diorite  are  occasionally  to  be  seen  breaking 
through  granite.  Diorites  are  generally  more  or  less  irregu- 
larly jointed,  but  in  some  instances  a  rude  columnar  struc- 
ture is  developed.  Sometimes  the  diorites  show  a  concen- 
tric spheroidal  structure  when  weathered.  The  selvages 
of  dikes  abound  in  schistoid  structures  parallel  to  the  dike- 
walls,  and  there  is  sometimes  a  quite  sharp  line  of  demarka- 
tion  between  the  massive-granular  and  the  schistoid  parts. 
Passages  between  quartz-diorites,  mica-diorites,  etc.,  may 
occasionally  be  seen,  and  the  different  varieties  appear  to 
be  mere  local  differentiations  of  the  same  rock.  Diorite  is 
also  reported  as  passing  (in  the  same  mass)  into  picrite,  and 
at  Cortlandt,  N.  Y.,  it  passes,  in  a  dike,  into  hornblendite. 
It  is  found  in  Sweden,  Finland,  the  Urals,  Austria, 
Saxony,  Bohemia,  the  Thuringian  Forest,  Odenwald, 
Schwarzwald,  Vosges,  Hungary,  Switzerland,  Italy,  Corsica, 


ig  MANUAL    OF  LITHOLOGY. 

France,  Spain,  Great  Britain,  Greenland,  Asia,  South  Africa, 
Canada,  and  in  the  United  States  at  Cortlandt,  Ft.  Mont- 
gomery, and  in  Orange  County,  N,  Y. ;  Deckertown,  N.  J. ; 
Kennebunkport,  Me. ;  Livermore  Falls  and  Dixville  Notch, 
N.  H. ;  the  valley  of  Lake  Champlain,  Nevada,  California, 
Yosemite  Park,  Michigan,  Minnesota,  and  Alaska.  The 
principal  mass  is  coarse- to  medium- and  uniform  fine-grained; 
microcrystalline  with  faint  glimmer,  and  colored  dark  green 
to  black,  and  compact,  black,  and  basaltic.  The  medium 
fine-grained  state  has  been  called  "  microdiorite  "  in  some 
cases,  as  analogous  to  "  microgranite,"  "  microsyenite." 
These  are  not  separate  rocks,  but  states  peculiar  to  the 
manner  of  cooling.  In  the  following  varieties  hornblende 
is  never  absent,  and  the  other  black  bisilicates  never  pre- 
dominate: 

I.  Hornblendt-diorite,  or  typical  diorite. 
II.  Mica-diorite. 

III.  Diorite-porphyrites. 

IV.  Diorite-aphanite. 

I.  DIORITE  (Haiiy). 

A  usually  granitoid  compound  of  oligoclase  (sometimes 
andesine,  labradorite,  or  anorthite)  and  hornblende, 
with  mica,  pyroxene,  and  quartz,  occasionally  ortho- 
clase,  usually  apatite,  and  ordinary  and  titaniferous 
magnetite. 

Silica  45-63  ;  Gr.  2.6-2.95. 

This  varies  in  texture  according  as  the  rock  is  in  large 
<or  small  masses.  In  bosses  it  is  coarse-grained  in  the  center, 
in  dikes  usually  uniformly  fine-grained  (like  aplite),  and  in 
ismall  dikes  or  on  the  selvages  of  some  large  ones  and  of 
.bosses  it  is  compact.  The  color  is  usually  greenish,  and 
•on  this  account  the  rock  was  formerly  classed  (with  dia- 
base and  gabbro)  as  a  "greenstone."  The  absolutely 


PRIMARY  ROCKS.  197 

compact  states  in  small  dikes  are  black  and  basaltic.  It 
is  frequently  porphyritic,  globuliferous,  and  sometimes 
drusy,  rarely  amygdaloidal,  and  by  squeezing-  is  altered 
frequently  to  hornblende-schist.  Plagioclase  is  usually 
oligoclase,  anorthite  causes  a  distinct  variety,  and  ande- 
sine  and  labradorite  are  sometimes  predominant.  The 
color  is  usually  white  with  yellowish  or  greenish  shades — 
occasionally  reddish.  The  luster  is  as  frequently  dull  as 
strong,  and  when  fresh  they  lack  the  glassy  habit  of  ande- 
sine  in  the  andesites,  though  they  may  be  transparent. 
They  are  not  so  perfectly  crystallized  as  are  the  orthoclases, 
and  usually  occur  in  regular  and  tabular  forms  with  abun- 
dant twinnings ;  but  the  angles  are  more  rounded  and  the 
granular  habit  more  prominent.  Hornblende  is  the  ordi- 
nary black  mineral  with  shades  of  green ;  in  stout  prisms 
or  grains,  sometimes  in  lath  shapes,  acicular,  and  in  irregu- 
lar patches ;  strong  luster  on  cleavages.  By  transmitted 
light  it  shows  greenish  shades,  and  thus  differs  from  the 
brown  basaltic  form,  which  occasionally  occurs — especially 
in  the  porphyritic  and  basic  varieties.  The  brown  color  is 
generally  associated  with  the  stout  crystals,  and  the  green 
with  the  lath  and  acicular  shapes.  It  alters  to  viridite,  ser- 
pentine, chlorite,  and  epidote,  which  accounts  *or  the 
greenish  color  of  the  rock,  and  allows  us  to  suppose  that 
the  original  color  was  black  or  gray.  The  only  essential  in 
this  variety  is  mica,  but  it  occurs  more  prominently  in  the 
quartz-diorites  (as  would  be  supposed).  It  is  biotite.  The 
other  minerals  are  only  accessory.  Quartz,  when  promi- 
nent, forms  quartz-diorite.  It  is  then,  as  already  stated,  in 
(M)  rounded  or  angular  crystalline  grains,  but  in  the  por- 
phyritic states  shows  sometimes  double  pyramids,  and  is 
generally  more  idiomorphic.  Pyroxene  cannot  be  depended 
upon.  In  many  localities  it  is  wanting,  and  when  abundant 
forms  pyroxene-diorite  ;  when  highly  predominant,  diabase. 


198  MANUAL    OF  LITHOLOG  Y. 

As  the  basic  component  it  is  usually  idiomorphic.  It  is 
found  (m)  in  the  groundmass  of  some  diorite-porphyrites. 
Orthoclase  frequently  occurs  (;«),  but  more  especially  in  the 
quartzose  varieties,  and  forms  micropegmatite  with  quartz. 
Apatite,  magnetite,  olivine,  and  orthite  are  usually  present 
and  (m) ;  titanite,  garnet,  and  tourmaline  are  (M),  and  the 
last  two  especially  in  the  quartzose  mica  varieties.  Diorite 
differs  from  syenite  in  having  plagioclase  for  orthoclase  ;  in 
its  greenish  (rather  than  red)  color;  its  prominent  horn- 
blende on  a  weathered  surface  (by  loss  of  feldspar) ;  by  the 
fusibility  of  the  feldspar,  and  the  greater  specific  gravity. 
It  differs  from  the  granulitic  gabbros  by  having  hornblende 
instead  of  pyroxene ;  by  its  lower  density ;  and  by  its  less 
strong  effervescence  with  acids  when  fine-grained  or  com- 
pact, owing  to  the  greater  proportion  of  secondary  calcite 
in  the  gabbros.  Some  authorities  place  the  coarse-grained, 
fine-grained,  porphyritic,  and  similar  states  of  diorite  in 
separate  divisions  ;  but  these  are  found  more  or  less  with 
all  occurrences,  and  can  be  readily  noted  in  the  field,  as 
they  have  the  same  mineral  composition.  The  following 
varieties  have  been  noted  : 

1.  Leuciite   is   only   a   fine-grained   dike-form   from  the 
Melibocus. 

2.  Scapolite-diorite.     An  altered  gabbro  from  southern 
Norway,  where   plagioclase   is   almost   entirely  altered  to 
scapolite,  and  pyroxene  uralitized.     It  is  also  found  along 
the  Ottawa  River  in  Canada. 

3.  Anorthite-diorite,  Corsite  (Zirkel).      A  diorite  com- 
posed of  anorthite  and  some  oligoclase,  blackish-green  horn- 
blende and  some  quartz.     Silica  48 ;   Gr.  2.76.     Named  by 
Zirkel  from  its  abundance  in  Corsica. 

(a)  Orbicular  Diorite,  Napoleonite.  A  variety  of  the 
above  where  the  components  form  alternating  concentric 
layers  about  kernels.  The  kernels  consist  either  of  anorthite 


PRIMARY  ROCKS.  1 99 

or  hornblende,  or  both,  and  they  likewise  show  a  radial 
structure.  The  balls  are  from  one  to  three  inches  in  size, 
and  a  section  shows  alternating  rings  of  light  and  dark 
color.  It  is  found  near  Ajaccio,  Corsica.  This  is  accepted 
as  a  peculiar  arrangement,  but  not  as  a  new  compound,  and 
thus  has  no  claims  to  be  a  separate  species. 

4.  Labradiorite.     A  diorite  where  labradorite  replaces 
oligoclase.     Silica  47-50;  Gr.  2.7-2.9.     This  has  no  claims 
to  be  classed  as  a  separate  rock,  as  Tschermak's  theory  of 
plagioclase   allows   all   variations   between   oligoclase   and 
labradorite  to  occur  in  diorite. 

5.  Hemithrtne  (Brongniart).  Kalkdiorit  (Senft).     A  name 
given  by  Brongniart  to  rocks  composed  of  hornblende  and 
calcite,  part  of  which  are  now  found  to  be  diorites.     In  any 
case  the  calcite  is  an  alteration  product.     Senft's  rock  is  a 
dark-green  compound  of  oligoclase,  hornblende,  and  mica 
with  calc-spar.     The  French  rock  is  from   the  Auvergne ; 
the  German  variety  from  the  Thuringian  Forest. 

II.  MICA-DIORITE  (Delesse),  Biotite-diorite. 
A  uniformly  granular  compound  of  oligoclase  or  andesine, 
orthoclase,  biotite  in  irregular  folia,  brown  and  green 
hornblende,  pyroxene   (augite   or   hypersthene),  and 
quartz  in  rounded  or  angular  grains.     Generally  of  a 
dark  color  and  almost  black. 
Silica  47-59  ;  Gr.  2.65-2.89. 

It  occurs  in  bosses  and  dikes  in  crystalline  schists  and 
older  sediments;  rarely  in  surface  extrusives.  It  is  found  in 
the  Tyrol,  Frankenwald,  France,  Norway,  Mexico,  Califor- 
nia, the  Pah-Ute  range,  Cortlandt,  N.  Y.,  etc.  V.  Cotta 
objects  to  calling  this  a  diorite  on  account  of  its  orthoclase. 
It  is  a  transition  to  quartz-mica-diorite,  and  that  to  granite, 
as  already  stated  (p.  187).  The  plagioclase  is  sometimes 
altered  ;  the  hornblende  more  often  brown  than  green,  and 


2OO  MANUAL    OF  LITHOLOGY. 

altered  to  chlorite  and  epidote.  Augite,  when  present,  is 
altered  to  chlorite,  calcite,  and  ores,  rarely  uralitized. 
Hypersthene  is  sometimes  altered  to  bastite.  Garnet  is 
accessory.  Its  fine-grained  form  is  like  kersantite  without 
calcite. 

III.  DIORITE-PORPHYRITES. 

As  stated  on  p.  178,  a  porphyrite  is  a  rock  with  a  compact 
matrix  of  plagioclase  and  exhibiting  phenocrysts.  It  differs 
from  a  porphyry,  which  is  a  compact  rock  of  orthoclase  or 
orthoclase-quartz  mixture.  The  porphyrites  can  be  divided 
according  to  their  content  of  the  black  bisilicates.  The 
mica-porphyrites  have  already  been  described,  and  the  mix- 
ture with  pyroxene  forms  the  gabbro-porphyrites.  Those 
with  hornblende  will  follow  here  as  diorite-porphyrites. 
These  can  be  divided  into  : 

1.  T)\or\te-porphyrite. 

2.  J/zVtf-diorite-porphyrite. 
3. 


I.  DIORITE-PORPHYRITE,  Hornblende-porphy- 

rite. 

In  a  groundmass  (described  on  pp.  180,  202,)  are  pheno- 
crysts of  hornblende,  also  plagioclase  and  mica.    The 
groundmass  weathers  lighter. 
Silica  39-65  ;  Gr.  2.6-2.7. 

It  occurs  in  sheets  and  dikes  in  Asia,  Africa,  central 
and  eastern  Europe,  Scotland,  the  New  England  States,  and 
Nevada.  Its  states  resemble  those  of  the  porphyrites  and 
mica-porphyrites,  and  with  the  above  occurrences  are  vesic- 
ular states,  tuffs,  etc.  The  vesicles  are  sometimes  empty 
and  sometimes  filled  with  green  earth,  calcite  ;  and  in  some 
localities  the  amygdules  form  the  greater  part  of  the  mass. 
The  rock  is  usually  irregularly  jointed  and  fissured  ;  rarely 
columnar  or  tabular.  It  is  not  so  abundant  as  the  more  acid 


PRIMARY  ROCKS.  2OI 

porphyrites.  Plagioclase  phenocrysts  are  white,  yellowish, 
or  reddish,  and  usually  dull.  Hornblende  is  in  irregular 
stout  prisms  or  acicular  shapes,  and  brownish  black.  Biotite 
is  in  hexagonal  tables,  seldom  in  folia.  Quartz  is  rare. 

.(The  first  three  types  following  are  entirely  dependent 
on  (m)  characteristics.) 

(a)  Suldenite,  Andesitic  Porphyrite  (Stache  and  v.  John). 
From   the  Suldenfern  in  the  Ortler  Alps,  with  54-62  silica. 
The  groundmass  is  light  to  dark  gray,  with  (m)  phenocrysts 
of  black  hornblende  (prisms) ;  (m)  plagioclase  and  orthoclase 
in  small  amount,  with  accessory  augite,  biotite,  and  quartz. 

(b)  Ortlerite,  Greenstone-porphyrite  (Stache  and  v.  John). 
From  the  Ortler  Alps,  with  silica  48-54.     Blackish-green  to 
grayish-green  groundmass,  fresh  glassy  black  prisms  of  horn- 
blende  (4-6    mm.),   and    sometimes  in   bundles.      Part   of 
Gumbel's  nadeldiorit,  from  eastern  Bavaria,  is  placed  here 
by  Zirkel. 

(c)  Propylitic  Porphyrite  (Stache  and  v.  John).     From  the 
Ortler  Alps,  with  silica  52-57.     Blackish-green  to  grayish- 
black    groundmass    of   monotonous    appearance,   carrying 
phenocrysts  of  plagioclase  (with  orthoclase)  in  abundance,, 
always  hornblende  (mostly  mixed  with  chlorite,  epidote,  and 
calcite) ;  biotite  is  only  accessory. 

(a)  Porfido-rosso-antico.  From  the  west  coast  of  the  Red 
Sea,  in  a  dike  in  granite.  This  is  the  famous  red  porphyry 
of  history.  In  a  blood-red  (M)  compact  groundmass  are 
abundant  small  snow-white  or  rose-red  striated  plagioclase 
phenocrysts  and  lustrous  black  acicular  hornblendes,  with 
usually  small  scales  of  specular  hematite.  Quartz  occurs  in 
irregular  veins,  never  in  regular  primary  grains.  Silica  64. 


2O2  MANUAL    OF  LITHOLOGY. 

2.  MICA-diorite-porphyrite. 

In  a  typical  porphyrite  groundmass  are  phenocrysts  of 
oligoclase  and  orthoclase,  with  hornblende  and  mica 
in  equal  proportions. 

Silica  61  ;  Gr.  2.6-2.7 

This  occurs  as  a  transition  between  the  hornblende-  and 
mica-porphyrites,  and  is  found  with  porphyrites  of  both 
species.  It  is  especially  found  in  the  Saar-Nahe  district,  the 
central  Alps,  in  China,  and  elsewhere. 

3.  DIORITE-APHANITE. 

A  greenish-gray  to  black  (m),  holocrystalline  to  compact 
groundmass  similar  to  those  noted  on  pp.  180,  200, 
and  carrying  few  or  no  phenocrysts. 

The  term  aphanite  was  applied  to  a  mass  so  compact 
that  its  constituents  could  not  be  resolved  with  a  lens,  and 
whose  color  was  green  to  black.  It  was  the  compact  state 
of  the  "  greenstones,"  diorite,  diabase,  and  gabbro.  The 
same  term  is  still  employed  to  denote  the  compact  state, 
which  bears  to  the  granular  states  the  relation  that  basalt 
does  to  dolerite. 

The  silica  and  specific  gravity  are  as  in  the  diorite-por- 
phyrites,  and  this  may  be  said  to  be  their  clear  groundmass. 
Jt  is  recognized  mainly  by  its  actual  association  with  diorite. 
Its  bulk  analysis  will  vary  so  that  it  may  approach  and  equal 
that  of  many  diabase-aphanites,  but  its  specific  gravity  is 
generally  lower.  It  carries  a  much  lower  amount  of  calcite 
than  does  diabase-aphanite,  and  will  not  effervesce  so 
strongly.  It  occurs  at  Bischofswerda,  Saxony,  and  else- 
where, in  narrow  dikes  and  apophyses  from  dioritic  dikes 
and  bosses. 


PRIMARY  ROCKS,  2O$ 

GROUP  14.     PYROXENE-ANDESITE. 

IIIc.  PYROXENE-ANDESITE-DIORITE  EXTRUSIVES. 
(Necessary  minerals!  Plagioclase,  hornblende,  and  a  pyroxene.) 

PYROXENE-ANDESITE. 

An  andesite  containing  abundant  pyroxene. 
Silica  50-68  ;  Gr.  2.72-2.8. 

Pyroxene-andesite  is  the  mineralogical  equivalent  of 
basalt.  It  is  more  than  that,  as  it  is  seen  passing  into  basalt 
at  Lowenberg  in  the  Siebengebirge,  where  the  so-called 
"  trachydolerite "  shades  into  augite-andesite,  and  this  by 
the  acquisition  of  a  somewhat  higher  olivine  content  be- 
comes basalt.  At  Arran,  Scotland,  augite-andesite  passes 
into  tholeite  (with  intersertal  texture),  and  that  by  still 
further  crystallization  of  the  groundmass  into  diabase. 
Augite-andesite  is  therefore  a  transition  between  horn- 
blende-andesite  and  the  gabbros.  As  an  appendix  to  this 
group  will  be  placed  the  so-called  "  propylite  "  and  "  quartz- 
propylite."  The  majority  of  authorities  recognize  these 
•only  as  peculiarly  metachemized  states  of  a  number  of  dif- 
ferent rocks ;  but  the  name,  as  Rosenbusch  suggests,  is 
"valuable  as  distinguishing  those  alterations.  Pyroxene- 
andesite  can  be  divided  into : 

I.  PYROXENE-<m&zs\te  (Zirkel).    Plagioclase  and  one  of 
the  pyroxenes. 

(a)  ^ogV/^-andesite  (Roth).     Plagioclase  and  augite. 

(b)  Diatlage-andesite  (v.  Drasche).     Plagioclase  and  dial- 
lage. 

(c)  ffyfierstkene-andesite.     Plagioclase  and  hypersthene.  , 
(</)  Enstatite-andesite  (Koto).     Plagioclase  and  enstatite. 
(e)  Olivine-pyroxene-zridesite. 

II.  PYROXENE-andesite  glass. 


204  MANUAL    OF  LITHOLOGY. 

\\\a.  PROPYLITE,  a  metachemized  state  of  diabase, 
diorite,  or  any  of  the  andesites,  due  to  solfataric  action. 

b.  Quartz-propylite,  a  similar  state  of  any  of  the  quartz- 
ose  varieties  of  the  above,  and  of  quartz-porphyry  of  the 
Washoe  type. 

I.  AUGITE-ANDESITE  (Roth). 

A  dark-colored  groundmass  varying  from  glassy  to  tra- 
chytic,  composed  of  (m)  plagioclase,  augite  (mono- 
clinic,  rhombic,  or,  infrequently,  triclinic),  carrying 
(M)  phenocrysts  of  plagioclase,  hypersthene  (and 
rarely  augite),  scanty  hornblende,  tridymite,  quartz 
seldom,  biotite,  and  olivine. 

Silica  56-68  (average  60) ;  Gr.  2.72-2.74. 

It  occurs  in  lava  sheets  and  streams,  and  in  dikes,  widely 
spread  among  the  active  volcanoes  of  Europe  and  Asia, 
Azores,  South  and  Central  America,  and  in  the  Great  Basin 
of  the  United  States.  The  famous  eruption  of  Krakatoa. 
extruded  great  amounts  of  this  rock,  so  that  the  floating 
pumice  hindered  navigation  in  the  Sunda  Straits  for  several 
days,  and  the  ashes  were  scattered  so  widely  and  profusely 
that  thirty  tons  were  shoveled  from  the  deck  of  an  Ameri- 
can ship  sixty  miles  distant.  Zirkel  notes  four  types  of  the 
rock: 

(1)  Semivitreous ;  luster  waxy,  pitchy  ;  color  more  nearly 
deep  brown  than  greenish  black  ;  sometimes  compact,  some- 
times fine-porous ;  groundmass  carrying  a  few  phenocrysts 
of  whitish  or  yellowish  feldspar.     This  is  the  type  in  North 
and  South  America,  Hungary,  Java. 

(2)  Less   characteristic   and  widely  distributed ;  is  like 
hornblende-andesite,  or  the  light  basalts,  as  in  Japan.     A 
gray   or  dark-brown  groundmass,   somewhat    porous   and 
"  coarse  porphyritic,"  with  (M)  phenocrysts. 

(3)  A  more  extended  type  (trachytic) ;  light  grayish  red ; 


PRIMARY  ROCKS.  2O$ 

rough ;  somewhat  porous ;  carrying  the  ingredients  in  the 
pores  as  crystals.  In  Hungary,  Mexico,  Italy. 

(4)  A  light-weight,  gray,  and  porous  groundmass,  carry- 
ing specular  iron,  and  biotite  in  the  pores,  as  in  the  lava  of 
Auvergne  (Little  Puy  de  Dome). 

The  plagioclases  are  stout  tabular,  and  twin  in  the  Carls- 
bad and  Baveno  types.  They  are  andesine  to  anorthite, 
mostly  fresh,  but  weather  to  opaline  masses  and  epidote. 
Sanidine  also  appears  in  small  amounts.  Augite  is  abun- 
dant (m),  but  infrequent  (M\  and  yellowish  to  greenish 
brown  by  transmitted  light ;  usually  fresh  in  the  rocks  with 
glass  base.  Rhombic  pyroxene  is  usually  hypersthene  in 
slender  needles,  sometimes  enstatite  and  bronzite,  sometimes 
the  triclinic  variety,  sometimes  diallage.  Hornblende  is 
not  so  frequent  or  abundant  as  in  the  other  variety  of  ande- 
site,  and  generally  occurs  only  in  a  few  large  prisms.  Bio- 
tite is  infrequent;  quartz  in  a  few  cases  (M)  and  2  mm., 
generally  (m) ;  tridymite  more  frequent  than  quartz  in  both 
pores  and  groundmass  ;  olivine  infrequent  (mainly  occurring 
when  augite  increases  and  rhombic  pyroxene  diminishes). 

Judd  describes  the  weathering  of  augite-andesite  as 
having  four  phases:  (i)  the  conversion  of  augite  to  viridite ; 
{2)  the  formation  of  opacite  ;  (3)  the  hydroxidation  of  opacite 
to  red  or  brown  ferrite,  to  form  the  tints  that  color  all  por- 
phy rites ;  (4)  the  kaolinization  of  feldspar,  and  formation  of 
calcite  and  chalcedony.  The  result  is  a  tuff.  Emmons 
states  that  tridymite  is  found  in  the  cavities  and  clefts  of 
the  partly  weathered  rock,  and  more  rarely  opal.  When 
weathering  advances,  the  reddening  of  the  groundmass  takes 
place,  and  the  fluxion  structure — not  seen  in  the  fresh  rock 
— appears.  The  feldspar  remains  fresh  while  the  red  color 
iades  to  pink,  and  this  to  yellowish  gray,  and  then  kao- 
linizes,  while  the  black  bisilicates  bleach  and  disintegrate. 


2O6  MANUAL   OF  LITHOLOGYS, 

The  rock  in  some  localities  shows  a  white  crust  on  weather- 
ing, while  the  interior  is  dark. 

1.  Oar^-augite-andesite     (Tschermak),     when     the 
quartz  is  in  phenocrysts  and  also  in  the  groundmass.     Silica 
63-65  ;  Gr.  2.61.     Found  in  South  America,  New  Zealand, 
Japan. 

2.  Mijakite  (Petersen).     From  the  island  of  Mijakeshima, 
Japan.     An  andesite  where  the  pyroxenic  mineral  is  (m)  in 
short  pellucid  columns,  and  is  triclinic,  like   babingtonite. 
An  American  triclinic  pyroxene-andesite  is  also  reported. 

lb.  Diallage-andesite.  From  the  Smrkouz  Mountains, 
Steiermark.  A  dark-brown,  fine-grained  rock  with  numer- 
ous phenocrysts  of  plagioclase  and  darker  foliated  crystals 
of  diallage.  A  similar  rock  occurs  in  Bohemia.  Some 
authorities  place  ophite  here. 

lc.  Enstatite-andesite.  With  enstatite  more  or  less 
abundant  and  monoclinic  pyroxene ;  generally  weathered. 
Bronzite  is  reported  in  one  variety  from  Japan.  Occurs 
there  and  in  South  America  and  New  Zealand. 

Id.  Hypersthene-andesite.  This  mineral  is  found  in 
many  andesites  in  slender  (m)  prisms,  frequently  altered — 
sometimes  to  bastite,  and  sometimes  to  fibrous  hornblende. 
It  is  frequently  (M)  in  great  individuals.  The  rock  occurs 
in  Japan,  the  Caucasus,  Mexico,  Colombia,  and  the  Great 
Basin  of  the  western  United  States. 

\e.  Olivine-pyroxene-andesite.  It  is  a  dark-colored  (M) 
fine-grained  rock,  with  holocrystalline  groundmass  of  pla- 
gioclase, pyroxene,  and  magnetite,  with  phenocrysts  of  pla- 
gioclase and  olivine.  Here  part  of  the  so-called  "  trachy- 
dolerite "  with  olivine  would  be  placed.  This  rock  is 
transitional  to  basalt.  Found  in  South  America,  etc 

(NOTE.     Some  authorities  place  tholeite  here.) 


PRIMARY  ROCKS.  2O/ 

•  II.  PYROXENE- ANDESITE  GLASS. 

There  are  abundant  cases  of  vitreous  states  to  this  group 
in  connection  with  the  widespread  lavas  of  the  same. 

AUGITE-ANDESITE. 

1.  Pitchstone.     From  the  Caucasus,  Scotland. 

(a)  Felsite.      From    Eskdale,    Scotland.      A    devitrified 
pitchstone. 

2.  Perlite.     From  Japan. 

3.  Obsidian.     From    Armenia,   island   of    Melos,   Ardna- 
murchan,  Scotland,  island  of  Hokkaido,  Japan.     Silica  53- 
59.     Color  brownish  to  greenish  black. 

4.  Obsidian-/<9r///jj/rj/.     From  Mount  Ararat,  with  silica 
77 ;  carrying  numerous  phenocrysts  of  plagioclase  and  dirty 
green  biotite ;    found    in  connection    with    a    rock    of  this 
class.     From  Hokkaido,  Japan,  is  a  black  glass,  transparent 
on  thin  edges,  with  silica  74,  and  many  phenocrysts. 

5.  Pumice.     In  many  flows  as  a  more  or  less  thick  crust, 
and  in  large  masses  (as  from  Krakatoa).     It  has  the  vesicles 
filiform  and   carries  a  small  number  of  phenocrysts.     Im- 
mense masses  of  this  state  of  the  rock  blocked  the  Straits  of 
Sunda  after  the  eruption  of  Krakatoa.     Color  straw-yellow 
light  yellowish  gray.     Silica  61-71. 

BRONZITE-ANDESITE. 

Here  come  two  varieties  of  this  rock  with  and  without 
olivine : 

1.  Boninite,  Bronzite-limburgite  (Petersen  and  Kikuchi). 
A  glassy  state  with  no  feldspar  from  the  Peel  Island  group, 
near  Japan  ;  carrying  olivine  and  diallage-like  augite. 

2.  Sanukite  (Weinschenk).     A  dense  gray  or  black  rock, 
with  conchoidal  fracture  and  (m)  abundance  of  magnetite^ 
acicular  crystals  of  bronzite,  and  monoclinic  augite,  forming 
a  colorless  glass  with  infrequent  large  phenocrysts  of  pla- 


208  MANUAL    OF  LITHOLOGY. 

gioclase  and  garnet.  From  Sanuki,  Japan,  and  elsewhere  in 
that  country.  This  bears  to  andesite  the  relation  that  augit- 
ite  does  tq  basalt. 


PROPYLITE     (v.    Richthofen),    Greenstone 
Trachyte  (in  part). 

1116.  QUARTZ-propylite  (same  authority). 

A  fine-crystalline  rock  with  devitrified  base,  consisting 
of  a  feldspar  from  whicn  calcite  has  been  removed, 
and  a  light-green  mineral,  mostly  epidote,  which  is 
the  secondary  (or  even  later)  derivative  from  one  of 
the  black  bisilicates.  Always  soft  from  weathering. 

Silica  57-72  ;  Gr.  2.7-2.9. 

These  are  no  longer  classed  as  separate  rocks  by  all 
authorities.  Zirkel  still  holds  to  their  being  distinct  varieties. 
Propylite  is  the  country-rock  of  the  Comstock  lode,  and  is 
derived,  as  first  claimed  by  Wadsworth  and  later  shown  by 
Becker,  from  the  weathering  of  a  number  of  rocks  into 
which  it  can  be  traced.  The  black  bisilicates  of  these  rocks 
(hornblende,  augite,  and  mica)  uniformly  pass  into  a 
chloritic  mineral  which,  in  its  turn,  becomes  epidote  of  a 
vivid  yellow  tinged  with  green.  The  weathering  of  an- 
desite, augite-andesite,  diorite,  and  diabase  produce  what 
is  known  as  propylite  ;  while  the  same  process  in  their 
quartzose  varieties,  and  in  some  quartz-porphyries,  forms 
what  has  been  called  quartz-propylite.  It  also  occurs  in 
the  Western  Isles  of  Scotland,  the  Siebengebirge,  and  Hun- 
gary. Szabo  was  the  first  to  object  to  the  rock  on  the 
ground  that  it  was  a  solfataric  product.  In  1882  Becker 
reported  that  the  Washoe  rock  was  altered  as  above  stated. 
The  arguments  of  Zirkel  against  the  rejection  of  the  name 
for  a  distinct  rock  seem  to  fail,  as  the  want  of  an  andesitic 


PRIMARY  ROCKS. 

glass  base  in  propylite  may  be  due  to  the  fact  that  the 
original  rocks  had  none,  as  in  other  cases  ;  or  to  its  loss  by 
devitrification ;  or,  again,  in  the  general  wreck  of  the  rock, 
as  Emmons  reports  the  complete  kaolinization  of  an  augite- 
andesite  in  the  island  of  Capraja.  The  other  argument,  that 
propylite  is  not  found  as  a  decomposition  product  in  many 
andesite  regions,  may  be  answered  by  the  fact  that  solfa- 
taric  action,  which  produces  propylite,  is  not  common  ;  but 
in  this  case  propylite  is  directly  traced  into  rocks  of  vary- 
ing name.  Rosenbusch  remarks  that  the  name  may  be 
useful  to  denote  a  peculiar  kind  of  alteration  of  the  above 
rocks.  As  such  it  is  used  here. 

GROUP    15.     PYROXENE-DIOR1TE. 
IHc.  PYROXENE-ANDESITE-DIORITE  INTRUSIVES. 
(Necessary  minerals  :  Plagioclase,  hornblende,  and  a  pyroxene.) 

PYROXENE-diorite. 

A  transition  between  diorite  and  the  granulitic  gabbros, 
as  pyroxene-andesite  is  between  andesite  and  basalt.  The 
rock  is  more  basic  than  diorite  ;  hornblende  is  very  subor- 
dinate, and  the  plagioclases  more  basic  than  oligoclase. 
Olivine  becomes  more  prominent,  and  mica,  quartz,  and 
orthoclase  are  rare.  The  monoclinic  pyroxene  is  usually 
augite,  and  this  mineral  is  more  frequent  than  any  pyroxene. 
Diallage  is  rare.  The  augite  is  green  (sometimes  brown) 
and  idiomorphic  (also  in  grains).  Rhombic  pyroxene  is 
hypersthene  or  bronzite,  which  now  and  then  occur,  and  are 
more  or  less  altered  to  bastite.  Occasionally  quartz  is 
found  quite  abundant.  The  texture  varies  between  the 
holocrystalline  one  of  diorite  and  the  ophitic  one  of  diabase! 
Its  lower  specific  gravity  tells  it  from  diabase,  as  well  as  its 
association  with  dioritic  rocks. 


2IO  MANUAL    OF  LITHOLOGY. 

I.  AUGITE-diorite  (Zirkel). 

A  diorite  with  predominant  augite  (diallage  or  malaco- 
lite),  green  (and  generally  brown)  hornblende,  labra- 
dorite,  some  olivine  and  titanite. 
Silica  47-5  7;  0^2.7-2.98. 

It  is  found  in  Great  Britain  and  the  Channel  Islands, 
Argentine  Confederation,  Bohemia,  Norway,  Odenwald, 
Hungary,  the  Alps,  Sumatra,  the  Andes,  Minnesota,  and 
elsewhere.  Of  the  accessories,  titanite  is  (M),  olivine  rarely 
(M),  magnetite  and  apatite  (m). 

i.  Brown  Diorite,  when  hornblende  is  brown  and  basaltic. 
This  variety  is  usually  associated  with  pyroxene  rocks,  and 
tends  to  pass  into  gabbro  by  increase  in  pyroxene,  and 
into  pyroxenite  by  failure  of  feldspar  and  hornblende.  It 
is  associated  with  norite  and  passes  into  it,  and  also  into 
massive  brown  hornblendtite  at  Cortlandt,  N.  Y.  It  also 
occurs  in  a  few  localities  in  Europe,  and  at  Montreal, 
Canada.  This  color  is  common  in  porphyritic  diorites, 
camptonites,  etc.  As  accessories  are  apatite,  magnetite,  and 
hypersthene. 

II.  QUARTZ-augite-diorite. 

A  variety  of  the  above  carrying  more  biotite  and  quartz, 
and  less  olivine.  The  silica  content  is  higher  also. 
Sometimes  scapolite  occurs.  It  occurs  in  Brazil,  the 
West  Indies,  the  Andes,  etc. 

III.  HYPERSTHENE-diorite. 

A  coarse-  to  medium-grained  compound  of  plagioclase 
(sometimes  epidotized),  brown  hornblende,  and  hyper- 
sthene. The  latter  also  forms  concretions.  In  Portu- 
gal, West  Indies. 


PRIMARY  ROCKS.  211 

IV.  GABBRO-diorite  (Tornebohm). 

An  alteration  product  of  gabbro  and  norite  where  the 
pyroxene  has  uralitized.  In  Scandinavia. 

V.  CAMPTONITE  (Rosenbusch). 

(M)  a  rock  rarely  coarse-grained,  but  usually  dense 
hypidiomorphic  granular  compound  of  plagioclase, 
hornblende,  pyroxene,  mica,  with  occasional  olivine, 
and  carrying  phenocrysts  of  lustrous  (M)  rod-shaped 
basaltic  hornblende,  andesine,  magnetite,  and  weather- 
ing to  a  rusty  brown. 

Silica  39-54  ;  Gr.  2.7-2.9. 

This  rock  is  found  in  dike  and  surface  effusions,  and  is 
intermediate  between  the  diorites  and  diorite-porphyrites, 
and  between  the  diorite-porphyrites  and  the  melaphyres.  It 
was  placed  by  Rosenbusch  with  his  lamprophyres ;  but 
M.-Levy  and  Zirkel  have  relegated  it  back  to  diorite  on 
the  ground  of  the  impropriety  of  separating  dike- forms.  It 
generally  has  a  low  augite  content,  but  sometimes  has  a 
very  high  one.  Rarely  it  is  amygdaloidal.  It  is  placed 
with  the  augite-diorites  on  account  of  its  having  basaltic 
hornblende  entirely,  and  thus  coming  under  the  same  head 
as  "  brown  diorite  "  above.  It  was  first  noted  by  Hawes  at 
Campton,  N.  H.,  and  has  been  since  noted  in  the  Champlain 
valley  of  Vermont,  in  New  York,  Maine,  Montreal,  Canada, 
Sierra  Nevada  range  of  California,  U.  S.  Colombia,  Tyrol, 
south  Norway,  etc. 

i.  ^K^t'/^-camptonite.  From  near  Christiania,  Norway, 
and  near  Lewiston,  Me.  With  abundant  augite  and  much 
olivine,  so  that,  as  Kemp  reports,  it  forms  a  transition  to 
the  melaphyres. 


212  MANUAL    OF  LITHOLOG  Y. 

VI.  HORNBLENDITE  (Dana). 

A  coarse  to  fine  granitoid  (sometimes  compact)  blackish 
aggregate  of  compact  brown  hornblende,  which  is 
usually  a  paramorph  of  one  of  the  pyroxenes. 
Silica  46-49  ;    Gr.  3-3.1. 

A  dike-rock  of  rare  occurrence,  and  not  to  be  confounded 
with  the  metamorphic  massive  rock  called  amphibolite.  It 
is  sometimes  a  segregation  in  part  of  the  dike,  and  generally 
the  altered  form  of  a  pyroxenite,  as  above  stated.  It  occurs 
in  the  Cortlandt  (N.  Y.)  diorite  series,  Amador  and  Calaveras 
counties,  Cal.,  the  Argentine  Confederation.  Mica-horn- 
blendite  is  found  in  Nova  Scotia. 


PRIMARY  RQCKS.  2I3 


BASIC   DIVISION— PYROXENE   ROCKS. 

These  are  divided,  according  to  their  alkali  and  Ca-Na 
content,  as  follows : 

I.  ALKALI  SECTION: 

(a)  Groups  16  and  17.  Feldspathoids,  alkali  feldspar,  magnetite, 
olivine,  plagioclase,  amphibole,  mica,  quartz. 

Extrusives,  Nephelinite,  Leucitite ;  Intrusive,  liolite. 

(b)  Group  1 8.  Feldspathoids,  olivine,  magnetite,   alkali   feldspar, 
plagioclase,  amphibole,  mica,  quartz. 

Extrusives,    Nepheline,   Leucite,   and    Melilite   Basalts;   In- 
trusive, none. 

II.  ALKALI-LIME-SODA  SECTION  : 

(a)  Groups  19  and  20.  Feldspathoids,  plagioclase,  magnetite,  oli- 
vine, amphibole,  mica,  alkali  feldspar,  quartz. 

Extrusives,  the  Tephrites ;  Intrusive,  Theralite. 
(b}  Group  19  (con?).    Feldspathoids,  plagioclase,  olivine,  magnetite, 
amphibole,  mica,  alkali  feldspar,  quartz. 
Extrusives,  the  Basanites. 

III.  LIME-SODA  SECTION: 

Groups   21    and  22.     Plagioclase,  magnetite,  olivine,   amphibole, 
mica,  feldspathoids,  alkali  feldspar,  quartz. 
Extrusive,  Basalt ;  Intrusive,  Gabbro. 


214  MANUAL    OF  LITHOLOGY. 

GROUP    16.     NEPHELINITE-LEUCITITE. 

la.   NEPHELINITE  (LEUCITITE)-IIOLITE  EXTRUSIVES. 

(Necessary  minerals  :  Feldspathoids  and  pyroxene.) 

In  this  group  there  is  no  plagioclase  nor  olivine.  We 
distinguish : 

1.  Nephelinite,  where  the  feldspathoid  is  nepheline. 

2.  Leucitite,  where  it  is  leucite. 

I.  NEPHELINITE  (Rosenbusch). 
A  coarse-granular  to  compact  (usually  porous)  principal 
mass,  usually  bluish  to  dark  green,  or  greenish,  gray- 
ish,   or   pitch  black,    less   frequently  grayish    white, 
rarely  light  wine-yellow  ;  subgreasy  or  pitchy  luster  ; 
composed  of   nepheline  and  augite,  with  magnetite, 
apatite,  leucite,  haQyne,  and  melilite. 
Silica  41-47 ;  Gr.  2.9. 

This  occurs  as  slaggy  lava-streams  and  in  dikes  and 
plugs,  in  the  Erzgebirge,  near  the  lake  of  Laach,  in  Bohe- 
mia, Sweden,  Cape  Verdes,  South  Africa.  The  states  are  : 

(a]  Doleritic  Nephelinite.    A  coarse-grained  compound  of 
nepheline,  reddish-brown  augite  and  magnetite,  with  some- 
times sanidine,  with  the  interstices  filled  with  a  mixture  of 
them,  and  no  glass  base.     This  state  is  difficult  to  distinguish 
from  nepheline-dolerite,  as  the  olivine  in  the  latter  is  seldom 
readily  recognized  (M),  and  it  is  only  by  tracing  it  into  the 
basaltic  state  that  a  distinction  can  be  made.     A  small  pro- 
portion oi  olivine  would  make  this  a  nepheline-dolerite. 

(b)  Fine-grained  to  Compact  (Basaltic)  Nephelinite.     In  a 
•groundmass  colored  as  above,  and   rarely   without  pheno- 
crysts,  are  (M)  haiiyne,  green  and  brown  augite,  black  mica, 
.apatite,  magnetite,  and,  rarely,  melanite  ;  and  (m),  in  addi- 
tion, nepheline,  melilite,  leucite,  and  more  or  less  glass  base. 


PRIMARY  ROCKS.  2I5 

As  accessories,  hornblende  is  rare,  sanidine  and  olivine  spo- 
radic. The  haiiyne  is  often  half  an  inch  in  size  and  is  the 
predominant  accessory,  the  others  being  quite  subordinate. 
In  the  Erzgebirge  and  Bohemia. 

(c)  Camptonitic  Nephelinite  (Rosenbusch).  A  (m)  ground- 
mass  rich  in  hauyne  and  poor  in  nepheline,  with  augite, 
hornblende,  and  meliiite,  carrying  large  phenocrysts  of 
biotite  and  melanite.  It  also  carries  a  little  sanidine,  and  is 
found  in  the  region  about  the  Kaiserstuhl. 

2.  LEUCITITE,  Sperone  (Italian  local  name). 
In  a  usually  microcrystalline  to  compact  groundmass  of 
shades  of  gray  (from  very  light  to  black),  and  usually 
porous,  are  phenocrysts  of  (M)  leucite,  augite,  tita- 
nite,  and  magnetite  that  are  rarely  so  abundant  or 
so  large  as  to  make  the  rock  appear  doleritic.  As 
accessories  are  nepheline,  hauyne,  biotite  ;  sometimes 
meliiite  and  garnet. 

Silica  40-50  ;  Gr.  2.5-2.81. 

This  occurs  in  lava-streams  in  the  Eifel,  Erzgebirge, 
Bohemia,  abundantly  in  Italy,  Cape  Verdes,  Algiers,  and  in 
the  Leucite  Hills  of  Wyoming.  The  amount  of  leucite  and 
its  habit  vary  in  these  rocks.  When  it  is  prominent,  augite, 
magnetite,  and  titanite  are  less  so ;  in  other  rocks  all  are 
equally  prominent.  Leucite  varies  from  a  well-crystalline 
to  a  rounded  form,  and  when  the  latter  it  is  accompanied 
by  brown  augite  and  forms  basaltoid  leucitite ;  when  well 
crystallized,  the  augite  is  green  and  they  form  tephritoid 
leucitite  (both  states  are  (m) ). 

(a)  Lava  Sperone  (local  name).  From  the  Alban  Hills  and 
elsewhere  in  Italy.  A  light,  porous,  brownish  or  yellowish 
gray  rock  composed  of  small  grains  of  leucite  and  much 
smaller  crystals  of  yellowish  brown  garnet,  with  augite, 
hauyne,  biotite,  and  sometimes  magnetite  and  specular 


2l6  MANUAL   OF  LITHOLOGY. 

hematite ;  in  a  groundmass  of  leucite  and  augite,  with  some 
glass  base,  magnetite  and  sporadic  plagioclase. 

(b)  Haiiynophyre     (Rammelsberg).      From     the    volcano 
Vultur,  near  Melfi,  in  S.  Italy.     A  rough,  porous,  dark-gray 
to  black,  generally  fine-grained  groundmass,  composed  of 
abundant   (m)    leucite,    much   nepheline,    augite,    melilite, 
magnetite,    apatite,    scanty    sanidine,    some    olivine,    and 
black    magnesia-mica ;    carrying    phenocrysts   of    hauyne, 
augite  in  abundance,  and  some  olivine,  mica,  and  leucite. 
Silica  40-50;    Gr.   2.5-2.8.     The  hauyne   is   abundant,  and 
2-10  mm.;  blackish-gray  conchoidal  fracture  and  scaly  struc- 
ture ;   cleavable  when   sky-blue ;   sometimes  red  from   sec- 
ondary growths  of  sesquioxide  of  iron  ;  sometimes  colorless 
and   cleavable.     This   is  a  transition  between   nephelinite, 
leucitite,  and  a  similar  hauyne  rock,  as  it  contains  an  abun- 
dance  of   each.     Zirkel    puts   it   here,   Rosenbusch   under 
nephelinite,  and   Deecke  under   Rosenbusch's   "  nepheline- 
leucite-tephrite,"  as  a  haiiyne-melilite  variety.     If  the  feld- 
spar be  sanidine,  as  reported  by  Mann,  it  would  fall,  not 
under  tephrite,  but  under  phonolite.     This  is  a  good  exam- 
ple of  the  small  variation  in  mineral  content  that  is  neces- 
sary to  move  a  rock  from  one  species  to  another,  and  this  is 
a  good  example  of  the  meeting  of  the  black  bisilicates,  felds- 
spars  and  feldspathoids  in  one  rock.     It  is  a  transition  be- 
tween phonolite,  trachyte,  rhyolite  on  the   one  hand,   and 
basalt,  pyroxenite,  and  the  peridotites,  on  the  other. 

(c)  J/zVtf-leucitite.     From  Leucite  Hills,  Wyo.     A  light 
yellowish   gray,    very    fine-porous,  felsitic    rock,    showing 
only  stripings  of  bronzy,  brownish  ye/low,  and  brownish  red 
mica,     (m)  it   appears   as  a  crystalline-granular  compound 
of   predominant   leucite     and    some   augite,    with   a   small 
amount  of  magnetite,  apatite,  and  nepheline.     Silica  56.30. 


PRIMARY  ROCKS. 

GROUP  17.     IOLITE. 
la.  NEPHELINITE-IIOLITE  INTRUSIVES. 

(Necessary  minerals  :  Pyroxene  and  feldspathoids.) 

IIOLITE  (Ramsay  and  Berghell). 

A  coarse-  to  micro-crystalline  compound  of  elseolite  and 
augite  with  garnet  (iiwarrite). 
Silica  42.79  ;  Gr.  2.9. 

An  elaeolite-augite  rock  free  from  feldspar  and  olivine,  and 
considered  as  the  intrusive  equivalent  of  nephelinite.  It  oc- 
curs in  dikes  and  narrow  apophyses  in  the  liwarre  Mountains 
in  northern  Finland,  where  it  was  thought  to  be  an  elaeolite- 
syenite,  but  was  found  to  be  without  feldspar.  The  elaso- 
lite  is  fresh,  grayish  white  to  light  gray,  and  in  small  allotri- 
omorphic  grains  with  greasy-vitreous  luster.  Augite  is 
idiomorphic  (prisms  and  tables) ;  apatite  is  abundant.  The 
garnet  is  a  titaniferous  lime-iron  variety,  and  titaniferous 
melanite  is  common,  and  also  light-red  titanite.  Elaeolite 
alters  to  cancrinite  and  calcite.  In  the  mass  apatite  and 
elaeolite  are  equally  predominant.  Thirty-seven  per  cent  of 
the  rock  powder  is  soluble  in  acids. 

GROUP  18.     NEPHELINE-,    ETC.,   BASALTS. 
Ib.  FELDSPATHOID  BASALTS. 

(Necessary  minerals  :   Pyroxene,  feldspathoids,  and  olivine.) 

These  are  divided,  according  to  the  feldspathoid,  into : 

1.  Pyroxene,  olivine,  and  nepheline,  Nfpkeline-\>2S>oM. 

2.  Pyroxene,  olivine,  and  leucite,  Ziaiz/i-basalt. 

3.  Pyroxene,  olivine,  and  melilite, 


2l8  MANUAL   OF  LITHOLOGY. 

I.  NEPHELINE-basalt,  Anamesite,  and  Dolerite. 
A  coarse-  to  micro-crystalline  (and  compact)  compound 
of  nepheline,  augite,  and  olivine  (usually  of  dark  color) 
which  in  the  dolerites  shows  the  ingredients  plainly, 
but  in  the  basalts  usually  shows  (M)  olivine    alone, 
sometimes  augite.     As  (M)  accessories  are  sporadic 
hornblende  and  mica.    Plagioclase  is  generally  absent. 
Silica  38-45  ;  Gr.  2.89-3.22. 

This  occurs  as  widely  spread  in  the  old  world  (espe- 
cially in  Germany)  as  the  feldspar-basalts,  and  is  found  as 
surface  and  intrusive  sheets,  lava-streams,  plugs  and  dikes. 
In  the  United  States  it  is  rare,  and  the  basalt  state  is  reported 
from  Austin,  Tex.,  Kawsoh  Mountains,  Nev.  and  Elk 
Mountains,  Col.  The  term  dolerite  refers  to  the  coarse- 
crystalline  state,  anamesite  to  the  medium-  to  fine-crystalline 
state,  and  basalt  to  the  microcrystalline  to  compact  (see 
later  under  "  Feldspar-basalt ").  Nepheline  is  usually  well 
crystallized  and  apparent  in  dolerite,  but  only  (m)  in  basalt. 
In  some  cases  nepheline  forms  a  granular  and  sometimes  an 
irregular  interstitial  amorphous  filling  in  which  the  other 
minerals  appear,  as  in  phonolite,  and  it  readily  alters  to 
zeolites.  The  other  minerals  appear  as  in  basalt  (p.  227). 
The  principal  accessories  are  leucite,  hauyne,  and  melilite. 
These  sometimes  preponderate  to  form  their  own  types  of 
basalt.  Plagioclase  can  enter  in  a  slight  amount  without 
placing  the  rock  among  the  basanites  ;  a  withdrawal  of  both 
feldspar  and  feldspathoids  makes  it  a  limburgite,  and  a  loss 
of  olivine  forms  nephelinite. 

(a)  Nephilinitoid  Basalt  (Boricky)  is  a  basalt  in  whose  (m) 
groundmass,  instead  of  nepheline,  is  seen  a  colorless,  gray- 
ish white,  or  yellowish  white  substance,  which  reacts  like 
nepheline  by  polarized  light,  but  is  otherwise  unlike  it  and 
greatly  altered.  In  Bohemia.  (This  is  a  (m)  distinction 
and  cannot  be  made  (M ). 


PRIM  A  RY  RO  CKS.  2 1 9 

(b)  Noseanite  (Boficky).  A  nosean-rich  nepheline-basalt 
with  coarse,  medium,  and  fine  states.  In  Bohemia,  the  Eifel, 
-etc. 

2.  LEUCITE-basalt,  Anamesite,  and  Dolerite. 
A   usually    dark-gray,    sometimes    (M)    fine-crystalline, 
rarely    coarse-grained,    usually    microcrystalline    to 
compact  and    slaggy  groundmass    composed    of   (m) 
leucite,  augite,  magnetite,  and  olivine,  with  or  without 
glass  base,  and  carrying  (m)  and  sometimes  (M)  pheno- 
crysts  of  augite  and  olivine,  and  rarely  leucite. 
Silica  40-47  ;  Gr.  2.84-2.94. 

It  occurs  as  necks  and  lava-streams,  especially  devel- 
oped and  studied  in  the  Eifel,  Erzgebirge,  about  the  lake  of 
Laach,  and  in  Hesse,  Bohemia,  Sardinia,  Algiers,  Persia, 
Australia,  and  New  Zealand.  As  stated  above,  the  doleritic 
state  is  rare,  the  anamesitic  uncommon,  and  the  basaltic 
cannot  be  readily  told  by  inspection  from  feldspar-basalt,  as 
leucite  retreats  to  the  (m)  groundmass,  which  is  rarely  coarse 
enough  to  be  resolved  with  the  lens.  Leucite  occurs  some- 
times well  crystallized,  but  usually  irregular  and  rounded. 
In  the  groundmass  it  is  ill  defined,  and  thus  differs  (m)  from 
its  habit  in  tephrite.  Augite  and  olivine  occur  as  in  other 
basalts.  Nepheline,  melilite,  and  haiiyne  are  in  varying 
amounts,  and  form  transitions  into  the  other  basalts  of  the 
group.  Samdine  and  plagioclase  cannot  be  very  abundant 
without  forming  either  \euc\te-phonolite  or  basanite.  Biotite, 
apatite,  and  hornblende  also  occur  (the  last  abundant  in  a 
few  localities). 

(a)  Leucitoid Basalt  (Boficky).    A  companion  to  nephelini- 
toid  basalt.     Here  leucite  is  not  sharply  defined,  but  seems 
to  be  present  in  irregular  colorless  patches  in  the  interstitial 
spaces.     In  Bohemia. 

(b)  Peperin-basalt  (Boficky).     A  reddish  brown  to  brown- 


22O  MANUAL   OF  LITHOLOGY. 

ish  gray  clayey  or  weathered  groundmass  composed  (m)  of 
augite,  leucite,  nepheline,  magnetite,  and  rarely  olivine, 
carrying  large  well-defined  phenocrysts  of  augite,  horn- 
blende, and  rubellan.  It  is  found  at  Kostenblatt,  Bohemia, 
and  in  a  few  neighboring  localities.  It  is  probably  a 
hardened  mud-tuff  (whence  the  name). 

3.  MELILITE-basalt  (Stelzner). 

A  usually  greenish  black  (sometimes  grayish  black  or 
grayish  blue)  fine-crystalline  to  compact  groundmass, 
composed  of  (m)  melilite,  augite,  and  olivine,  and 
carrying  phenocrysts  of  (M)  olivine  and  augite,  rarely 
of  melilite,  and  (m)  of  the  same,  with  nepheline,  mag- 
netite, and  apatite. 

Silica  34-36  ;  Gr.  2.89-3.04. 

It  occurs  in  small  bosses ;  in  dikes  of  small  and  medium 
size ;  in  streams  and  tuffs.  It  is  especially  developed  in 
Swabia ;  also  in  Bohemia,  Saxony,  Sweden,  the  Transvaal, 
etc.,  and  in  America  at  Ste.  Anne,  Canada,  Manheim,  N.  Y., 
and  Uvalde  county,  Tex.  The  honey-yellow  melilite  is  gen- 
erally well  crystallized,  and  is  sometimes  large  enough  to  be 
distinguished  by  the  lens,  but  it  is  usually  (m)  and  forms  one- 
third  of  the  whole  rock.  Augite  and  olivine  as  in  the  other 
basalts,  and  frequently  the  latter  is  the  only  (M)  visible  phen- 
ocryst.  It  is  sometimes  altered  to  serpentine.  As  acces- 
sories occur  (m)  a  scattering  of  biotite  laminae  ;  nepheline 
usually  rare,  but  abundant  in  the  Canadian  rock  ;  native 
copper  is  found  now  and  then ;  picotite,  hauyne,  and  horn- 
blende are  rare.  This  ultra-basic  rock  is  found  breaking 
through  granite  and  other  rocks  of  high  acidity,  so  that  it 
has  not  lost  any  acidity  in  so  doing.  It  is  sometimes  drusy. 
Rosenbusch  has  named  the  dike-forms  on  the  island  of  Alno, 
Sweden,  alnoite.  Their  mica  (anorhite)  is  arranged  parallel 
to  the  selvages,  as  in  cases  already  noted  in  micaceous 


PRIMARY  ROCKS.  221 

dikes.     The   Canadian   rock   also   has  anomite,  and   much 
nepheline  and  perofskite. 

(There  are  no  intrusives  to  this  group.) 


ALKAU-LIME-SODA   SECTION. 

GROUP   19.     TEPHRITE-BASANITE. 
Ha.  TEPHRITE-BASANITE-THERALITE  EXTRUSIVES. 

(Necessary  minerals:  Feldspathoids,  plagioclase,  pyroxene,  with  or 
without  olivine.) 

(a)  Without  olivine,  the  tephrites  (v.  Fritsch). 

1.  Pyroxene,  plagioclase,  and  nepheline,  Nepheline-te^h.- 
rite. 

2.  Haiiyne,  Haiiyne-tephrite. 

3.  Pyroxene,  plagioclase,  and  leucite,  Leuctte-tephrite. 

(b)  With  olivine,  the  Basanites  (Brongniart). 

1.  Pyroxene,  plagioclase,  olivine,  and  nepheline, Nepheline- 
basanite. 

2.  Pyroxene,   plagioclase,   olivine,   and   leucite,  Leucite- 
basanite. 

ai.  NEPHELINE-tephrite 

A  generally  fine-crystalline  to  compact  (but  sometimes 
coarse  crystalline-granular  and  porous)  groundmass, 
sometimes  basaltic,  and  sometimes  of  greasy  luster ; 
light  gray,  grayish  green,  brownish  gray  ;  composed 
of  (m)  plagioclase,  augite,  and  nepheline  (sometimes 
with  leucite),  and  more  or  less  glass  base.  This  is 


222  MANUAL  OF  LITHOLOGY. 

sometimes  clear  of  phenocrysts,  and  sometimes  ex- 
hibits them  of  (M)  size,  of  the  components,  with  ac- 
cessory hornblende,  biotite,  sanidine,  and  hauyne. 
Augite  is  green  and  brown,  the  former  in  the  ground- 
mass  and  the  latter  as  phenocrysts.  Hornblende  and 
biotite  are  sometimes  abundant  and  (m) ;  sanidine  is 
rare  and  scarce ;  hauyne  is  blue  and  yellow. 
Silica  49-57 ;  Gr.  2.62-2.75. 

It  occurs  as  lavas-streams,  sheets,  plugs,  in  Germany,. 
Bohemia,  Africa,  Asia,  the  Canaries,  Cape  Verdes,  and  in 
the  Peloncello  Mountains,  Ariz. 

(a)  Buchonite  (Sandberger)  is  a  variety  with  a  (m)  nephe- 
line-plagioclase  groundmass  containing  microlites  of  augite,. 
carrying  abundant  long  black  prisms  of  hornblende,  nephe- 
line   with  greasy  luster,  (M)  biotite  and   plagioclase,  and 
sometimes  orthoclase.     Silica  54-84;  Gr.   2.85.     From   the 
Rhone  district  (Buchonia).     A  hornblende-nepheline-teph- 
rite. 

(b)  Phono  lit  e-te^\irite.     A  compact   glimmering   ground- 
mass  with  greasy  luster,  composed  of  a  moderate  amount  of 
plagioclase,  considerable  sanidine,  scanty  augite  and  horn- 
blende, and  carrying  phenocrysts  of  sanidine  and  hauyne. 

(c)  Tephritoid    (Bucking).      A     plagioclase-augite    rock 
without  olivine,  in  which  nepheline  cannot  be  recognized  as 
a  distinct  mineral,  but  whose  base  seems  to  carry  it,  from 
its  high  soda  content  and  its  gelatinizing  with  acids. 

a2.  HAUYNE-tephrite. 

A  dark-gray  to  black  groundmass  carrying  phenocrysts 
(visible  with  lens)  of  labradorite,  acicular  hornblende, 
augite,  dark-blue  hauyne,  or  waxy-yellow  nosean 
grains.  The  groundmass  contains  (m)  augite  in  abun- 
dance, with  titanite  and  apatite,  seldom  olivine.  From 
La  Banne  d'Ordenche,  and  near  the  lake  of  Gu£ry, 
France. 


PRIMARY  ROCKS.  22$ 

a$.  LEUCITE-tephrite. 

A  structure  like  nepheline-tephrite.  Fresh  and  weath- 
ered, and  altered  to  analcime.  In  a  light-gray,  bluish, 
or  greenish  gray  groundmass  (fine-grained  to  compact, 
and  rich  in  glass  base  or  without  it)  composed  of  (m) 
plagioclase  (sometimes  sanidine),  small  amounts  of 
leucite,  and  sometimes  nepheline,  augite,  magnetite, 
and  apatite,  are  phenocrysts  of  leucite  (sometimes  of 
large  size,  and  sometimes  altered  to  analcime),  plagio- 
clase, sanidine,  augite,  nepheline,  hauyne,  hornblende,, 
and  quartz,  and  (m)  melanite. 
Silica  46-58;  Gr.  2.57. 

It  occurs  in  lava-streams — infrequently  in  dikes — in  Ger- 
many, Bohemia,  Italy,  East  Indies.  The  leucite  is  usually 
in  well-defined  individual  grains — no  matter  how  minute  it 
may  be,  and  in  this  respect  it  differs  from  its  habit  in  the 
basalts,  where  it  is  much  more  irregular  and  fills  interstitial 
spaces  in  the  groundmass. 

(Hussak  places  here  the  rocks  of  Brazil,  Cape  Verdes^ 
and  at  Deckertown,  N.  J.,  which  carry  large  folia  of  biotite, 
and  rounded  bodies  which  are  sometimes  distinguished  as 
analcime  and  sometimes  as  calcite.  All  of  these  rocks  seem 
to  have  been  metachemized,  as  the  augite  has  uralitized,  and 
the  above  rounded  bodies  are  probably  altered  leucites.) 

bi.  NEPHELINE-basanite. 

This  rock  varies  between  nepheline-basalt  and  nepheline- 
tephrite.  It  resembles  basalt,  and  has  a  groundmass  of 
(m)  plagioclase  in  varying  proportions,  nepheline, 
augite,  and  olivine,  and  carries  phenocrysts  of  the 
same.  The  groundmass  may  be  (i)  basaltic  and  black 
or  brown,  composed  of  much  plagioclase,  black  augite, 
nepheline,  and  olivine,  with  small  amounts  of  glass,. 


224  MANUAL    OF  LITHOLOGY. 

and  not  many  accessory  minerals,  or  (2)  tephritoid  and 
greenish,  through  change  in  augite,  with  magnetite 
and  small  amounts  of  feldspar,  and  carrying  an  abun- 
dance of  accessories,  as  hornblende,  biotite,  titanite, 
hauyne,  and  sometimes  sanidine,  so  that  it  becomes 
phonolite. 

Silica  40-51;  Gr.  2.90-3.15. 

It  occurs  in  the  Eifel,  in  Bohemia,  Cape  Verdes,  Canaries, 
South  Africa,  Japan,  Uvalde  County,  Tex.,  Elk  Mountains, 
Col.,  etc.,  in  lava-flows,  and  weathers  to  a  yellowish  crust 
(somewhat  like  that  of  phonolite),  and  gelatinizes  with 
HC1. 

Basanitoid  (Bucking).  A  compound  of  plagioclase,  oli- 
vine,  and  augite,  and  with  no  perceptible  nepheline,  but 
with  a  base  that  gelatinizes  with  acids,  like  nepheline  com- 
pounds, and  has  a  high  soda  content.  It  occurs  along  the 
Rhone  and  south  of  the  Thuringian  Forest. 

b2.  LEUCITE-basanite,  Leucitophyre  (in  part). 
A  similar  rock  with  leucite  replacing  nepheline.  In  a 
glass  base  is  a  combination  of  (m)  leucite,  plagioclase, 
olivine,  and  magnetite.  Leucite  alone  is  commonly 
(M),  sometimes  green  or  black  augite;  the  others 
rarely,  and  nepheline  never.  The  texture  varies  from 
coarse-granular  to  compact  in  the  same  lava.  This 
was  formerly  included  with  leucite-phonolite  under 
the  name  leucitophyre. 

Silica  47.64;  Gr.  2.77-2.81. 

It  is  the  lava  of  Vesuvius,  and  also  found  in  the  Eifel, 
Brazil,  Java,  and  lower  California. 


PRIMARY  ROCKS.  22$ 

GROUP  20.     THERALITE. 

Ha.  TEPHRITE-THERALITE  INTRUSIVE. 

(Necessary  minerals  :   Feldspathoids,  plagioclase,  and  pyroxene.) 

THERALITE  (Rosenbusch). 

A  granitoid  to  compact  compound  of  augite,  plagioclase, 
and  nepheline,  with  olivine  as  accessory. 
Silica  43. 17;  Gr.  2.93. 

This  occurs  in  dikes,  bedded  sheets,  and  laccoliths  in 
the  Crazy  Mountains,  Mont.,  and  is  the  intrusive  state  of 
the  tephrites  that  was  looked  for,  and  the  name  is  given 
from  the  Greek  verb  "  to  be  sought  for."  The  augite  is  in 
prisms  up  to  \  inch  ;  biotite  in  sharp  hexagonal  tables  ;  an- 
orthoclase  and  nepheline  in  coarse-grained  aggregates; 
olivine  is  (M)  and  rust-brown.  In  the  largest  laccolith  the 
texture  was  granitoid  in  the  middle  and  became  compact  at 
two  feet  from  the  walls,  with  columnar-jointed  structure 
normal  to  them.  There  are  porphyritic  states  of  a  dark 
green  with  phenocrysts  of  black  augite,  and  abundant  olivine 
and  biotite.  A  similar  rock  has  been  noted  on  the  Elbe. 

Teschinite.  Rosenbusch  places  this  rock  here  as  the  leu- 
cite  equivalent  of  theralite,  as  the  analcime  is  its  representa- 
tive ;  but  the  microscope  shows  that  this  mineral  has  been 
formed  at  the  expense  of  labradorite.  For  the  description 
of  the  rock  see  under  "  Diabase." 

GROUP   21.     Ilia.  BASALT-GABBRO   EXTRUSIVES. 

///.   LIME-SODA   SECTION. 
(Necessary  minerals;  Plagioclase,  pyroxene,  olivine,  magnetite.) 

Following  the  analogy  of  the  former  divisions,  this  group 
will  be  separated,  according  to  the  predominant  member  of 
the  necessary  minerals,  as  follows : 


226  MANUAL    OF  LITHOLOGY. 

1.  Predominant  plagioclase,  Plagwclase-bzs&lt,  or  basalt. 

2.  Predominant  olivine,  Limburgite,  or  magma-basalt. 

3.  Predominant  pyroxene,  Augitite. 

DOLERITE  (Haiiy),  "  Deceptive." 
ANAMESITE  (v.  Leonhard),  "  Intermediate." 

BASALT   (Agricola),  Feldspar-basalt.     (From  the 

Latin  basaltes.) 

(M)  dolerite  is  the  coarse-grained,  anamesite  the 
medium  fine-grained,  and  basalt  the  microcrystal- 
line  to  compact  state  of  a  compound  of  (M)  plagio- 
clase and  augite,  with  (m)  magnetite,  and  olivine  (M) 
and  (m) ;  also  with  neither  nepheline  nor  leucite.  All 
the  states  exhibit  pores  and  vesicles,  but  the  last  is 
highly  vesicular  and  amygdaloidal. 

Silica,  dolerite,  48-57 ;  anamesite,  47-52  ;  basalt, 

40-51. 
Gr.  dolerite,  2.7-3';  basalt,  2.9-3.1  ;  average,  2.87. 

The  compound  occurs  widely  distributed  through  the 
world  as  a  basic  lava,  in  surface  and  intrusive  sheets,  lava- 
streams,  plugs,  and  dikes.  In  North  America  it  covers  ex- 
tensive areas,  and  especially  on  the  Pacific  border,  where  it 
forms  many  "  table  mountains  "  and  surface  sheets  many 
square  miles  in  area.  Basalt  especially,  and  anamesite  to  a 
much  less  degree,  are  traversed  by  planes  causing  columnar 
and  tabular  jointing.  This  is  especially  the  case  near  the 
margins  of  the  flows.  The  columnar  structure  is  well  de- 
veloped near  Orange,  N.  J.,  on  the  Columbia  River,  Ore., 
and  abroad  at  Fingal's  Cave,  the  Giant's  Causeway,  in 
Australia,  etc.  The  columns  are  straight  or  curved,  and 
horizontal,  vertical,  or  inclined,  dependent  on  the  direction 
of  the  flow,  as  the  jointing  is  normal  to  the  cooling  surface, 


PRIMARY  ROCKS.  22/ 

whether  that  be  the  air  or  the  dike-  or  bed- walls.  This 
structure  is  caused  by  the  contraction  of  the  cooling  mass, 
and  is  met  with  in  dike-rocks  and  their  walls.  The  tabular 
structure  is  similarly  caused,  and  divides  the  columns  near 
the  selvages  of  the  dikes.  This  is  sometimes  of  "  ball 
and  socket  "  form,  which  is  shown  on  a  grand  scale  near 
San  Francisco,  Cal.  This  last  is  probably  due  to  the 
same  forces  that  cause  spheroidal  weathering.  The  number 
of  sides  to  a  column  varies  from  three  to  eight.  The 
"  plugs  "  above  mentioned  are  the  filled  up  flues  of  extinct 
volcanoes. 

The  adjective  "  feldspar  "  is  applied  by  many  authorities 
to  this  mineral  combination,  to  show  that  it  does  not  contain 
nepheline  nor  leucite.  In  case  a  distinct  comparison  is  made 
between  the  basalts,  this  may  be  necessary ;  but,  as  the 
original  "  basalt  "  contains  that  mineral,  it  can  be  termed 
"  basalt,"  as  the  hornblende-syenite  is  simply  "  syenite.'* 
The  other  basalts  are  then  &^£*/*#i-basait,  &««V*-basalt,  etc. 
The  varying  states  (dolerite,  anamesite,  basalt)  are  due 
solely  to  differences  in  the  rapidity  of  cooling,  analogous  to 
the  differences  in  the  crystalline  texture  of  slowly  and  rap- 
idly cooled  abyssals.  In  a  thick  effusion  of  the  mixture  the 
interior  will  show  the  very  coarse  "  dolerite,"  which  will 
change  through  the  medium  grain  of  the  same  to  the  fine- 
grained "  anamesite,"  and  thence,  as  we  near  the  top  of  the 
flow  or  the  selvage  of  the  dike,  we  find  the  grain  becoming 
microcrystalline,  and  finally  reach  compact  "  basalt,"  where 
cooling  was  most  rapid.  The  surfaces  of  lava-flows  are 
characterized  by  vesicular,  slaggy,  and  pumiceous  states,  as 
already  noted ;  but  the  fluidity  of  the  effused  basalt  is  so 
great  that  some  of  the  vesicles  are  large  enough  for  the  tall- 
est man  to  stand  erect  and  extend  his  arms  without  touching 
the  interior,  as  in  some  Hawaiian  flows.  The  lining  of 
vesicles  and  the  selvages  of  dike-basalt  show  vitreous  states 


22%  MANUAL    OF  LITHOLOGY. 

(tachylite,  hyalomelane),  and  infiltration  into  the  vesicles  of 
old  lavas  forms  amygdaloidal  structures. 

As  dolerite  is  coarse-  to  medium-grained,  the  principal 
components  can  be  recognized  (M\  The  fresh  fracture 
shows  a  brilliant  surface.  The  plagioclase  is  usually  fresh  and 
white  or  light  gray,  and  occurs  in  tables,  blades,  irregular 
.grains,  and  rarely  in  prisms.  It  is  found  as  phenocrysts 
in  the  principal  mass  and  in  the  cavities,  and  is  usually 
labradorite,  but  varies  more  frequently  to  the  bytownite- 
.anorthite  end  of  the  series  than  to  andesine.  As  phenocrysts 
it  is  sometimes  an  inch  long.  Sanidine  occurs  sporadically 
at  times,  generally  (m),  but  sometimes  (M),  and  half  an  inch 
long  by  one  quarter  wide  (Lowenberg,  where  the  transition 
between  andesite  and  basalt  has  been  noted).  Augite  occurs 
in  stout  brownish  black  columns  or  grains,  sometimes  in 
laths.  It  is  brown,  brownish  red,  and  rarely  green  by  trans- 
mitted light.  In  the  groundmass  it  is  seldom  well  crystal- 
lized. Olivine  is  rarely  present  in  the  well-crystallized  states, 
-except  in  Iceland,  where  it  is  reported  to  be  occasionally  as 
abundant  as  the  augite,  and  of  a  semimetallic  luster  and 
.greenish  brown  color.  Magnetite  is  rarely  visible  to  the  eye 
in  any  of»the  rock  states,  but  titaniferous  magnetite  appears 
{M)  in  large  black  folia,  in  some  Hungarian  rocks,  and  half 
a  foot  across.  Apatite  (m)  is  rare  ;  large  greenish-yellow  or 
light  brownish-yellow  crystals  of  hornblende  infrequent,  and 
quartz  rare. 

As  anamesite  the  components  are  generally  fine-grained 
and  require  a  lens  for  distinction.  The  same  minerals  occur, 
and  in  about  the  same  proportion,  except  that  olivine  be- 
comes more  apparent  (m)  in  the  groundmass.  We  can 
detect  the  compound  character  by  the  naked  eye,  but  find  it 
ihard  to  resolve  it. 

In  basalt  the  conditions  are  different.  The  fresh  rock 
is  microcrystalline  (with  the  recognized  glimmer  on  a 


PRIMARY  ROCKS.  22$ 

fresh  fracture)  to  compact  and  homogeneous.  The  color  is 
generally  grayish  to  bluish  black,  seldom  greenish  black, 
dark  green,  or  dark  brown.  In  the  South  Mountain,  on  the 
border  of  Pennsylvania  and  Maryland,  the  ancient  basalts 
are  now  pale  green,  and  have  been  sheared  into  rocks  which 
were  thought  to  be  slates  until  the  late  Dr.  G.  H.  Williams 
demonstrated  their  igneous  origin.  The  fracture  is  uneven, 
splintery,  and  coarse-conchoidal  in  the  compact  states.  It 
often  carries  (M)  phenocrysts  of  olivine,  plagioclase,  augite, 
and  magnetite  in  crystalline  grains,  on  fresh  fractures  the 
last  shows  metallic  reflections  of  extreme  minuteness.  The 
groundmass  varies  from  holocrystalline  to  a  half-glassy 
state,  and  carries  few  phenocrysts  in  all  the  variations  be- 
tween granular  and  glassy.  The  altered  augite  forms  green 
earth,  chlorite,  and  calcite.  Olivine  is  oil-green  and  in 
angular  (M)  and  round  grains.  Hornblende  generally  as 
phenocrysts  and  (M),  (sometimes  f  inch),  and  yellowish 
brown  (brown  by  transmitted  light) ;  this  has  already  been 
noted  in  the  description  of  other  rocks  as  "  basaltic  horn- 
blende." Biotite  is  (M)  in  phenocrysts.  Some  authorities 
note  "  hornblende  "  and  "  mica  "  varieties  of  basalt.  Quartz 
is  in  (M)  grains  in  Europe  and  most  notably  in  the  western 
United  States,  where  many  authorities  have  commented 
upon  it.  All  agree  that  it  is  primary.  In  the  "  quartz- 
basalts  "  of  this  locality  it  is  one  of  the  oldest  crystalliza- 
tions, both  (M)  and  (m),  and  is  milk-white.  Among  the  (M) 
accessories  are  zircon,  bluish  sapphire,  blue  cordierite  in 
granular  masses  over  two  inches  long,  metallic  iron  (at 
Mount  Washington,  N.  H.,  Isle  of  Disko  (150  Ibs.)),  and 
an  olivine  compound,  in  irregular  shapes  and  varying 
sizes,  called  "  bombs."  These  last  are  peridotites,  and  are 
thought  by  some  to  be  segregations  of  the  magma,  and  by 
others  to  be  pyroclasts,  as  they  frequently  exhibit  sharp 
re-entering  angles.  They  contain  nepheline  in  nepheline- 


230  MANUAL    OF  LIT  HO  LOG  Y. 

basalts.  In  the  cavities,  cracks,  and  interior  vesicles  of 
basalt  are  numerous  secondary  minerals  from  metachemism, 
as  quartz,  chalcedony,  hyalite,  fire-opal,  semi-opal,  zeolites, 
carbonates,  of  lime,  magnesia,  iron,  etc.,  barite,  green  earth, 
delessite,  and  chlorophseite.  Epidote  is  rare.  Native  copper 
is  found  at  Lake  Superior  and  in  the  South  Mountain  of 
Pennsylvania  and  Maryland.  The  rock  weathers  to  a  rusty 
crust  of  lighter  color  than  the  interior,  and  the  angular 
edges  round  by  spheroidal  weathering.  This  sometimes 
proceeds  regularly  inwards  to  form  concentric  shelly  crusts 
when  the  rock  is  compact  and  not  much  jointed,  and  these 
can  be  separated  with  a  hammer ;  sometimes  weathering 
enters  along  the  joint  planes  so  as  to  form  irregular  poly- 
hedra,  that  fall  apart  on  fracturing,  after  the  analogy  of  ball 
and  socket  jointing.  In  this  case  the  weathering  is  uniform 
throughout.  The  state  thus  produced  by  the  variations  in 
color  is  called  "  spotted  "  or  "  granular  "  basalt.  The  first 
chemical  change  is  in  the  formation  of  carbonate  and 
oxide  of  iron,  which,  by  loss  of  carbonic  acid,  become 
ferruginous  tuffs  and  red  clays.  The  varieties  are: 

1.  Quartz-basalt  (Diller),  with  large  percentage  of  free 
quartz.     From  Lassens  Peak,  Cal.,  the  Eureka  district,  Nev., 
Tewan  Mountains,  N.  M.,  Santa  Maria  basin,  Ariz.,  Anita 
Peak,   Col.,  with   a  few   localities  in  Europe  where  small 
amounts  are  found.    The  quartz  is  in  milk-white  grains  with 
plagioclase,  augite,  and  olivine.      Iddings  reports  them  as 
distinctly   rounded,   and   suggests    that   they   are   the   un- 
absorbed  portion  of  the  original  mass,  in  which  they  were 
formed  by  the  action  of  moisture.     In  the  Tewan  locality 
both   quartzose   and   quartzless  forms  agree  closely,  with 
silica  52 ;  the  Lassens  Peak  variety  shows  silica  57.25. 

2.  Hyper sthene-bviS&lt  (Diller).     From    Mount  Thielson, 
Ore.      A    porous    basalt    with   a   groundmass    rich  in  (m) 
dark-brown  glass,  and  consisting  of  (m)  plagioclase,  augite, 


PRIMARY  ROCKS. 

magnetite,  and  apatite,  carrying  great  phenocrysts  of 
plagioclase,  hypersthene,  and  olivine.  Similar  rocks  are 
reported  from  Mount  Pitt,  Ore.,  and  from  San  Salvador.  A 
fironzite-basalt  is  reported  from  Greenland.  Silica  55.68; 
Gr.  2.64-2.88. 

3.  Parabasalt  (Zirkel),  Olivineless  Basalt.   Carrying  mono- 
clinic  and  rhombic  pyroxene  and  plagioclase,  but  without 
olivine,  nepheline,  or  leucite.     It  occurs  as  dolerite,  aname- 
site,  and  basalt,  in  Germany,  Sardinia,  Madagascar,  etc. 

4.  Analcimite  (Gemellaro).      A  highly  vesicular  basalt 
with  large  cavities  and  clefts  in  which  analcime  has  been 
•deposited  through  alteration  in  the  rock,  so  that  the  greater 
portion  of  the  mass  is  of  this  mineral.     From  the  Cyclopean 
Islands. 

BASALT  GLASS. 

Here  are  grouped  together  all  the  glassy  states  of  all  the 
basalts  noted,  and  of  any  mixture. 

BASALT   GLASS  (Judd  and  Cole). 
Tachylite  (Breithaupt).     An  extrusive  basic  glass  with 
conchoidal  fracture,  readily  soluble  in  HC1  (whence   the 
name). 

Hyalomelane  (Haussmann).  A  similar  glass  not  so 
.affected  by  acids. 

Both  types  are  found  in  glassy  states  of  all  the  basalts, 
so  that  they  cannot  be  divided  between  them  with 
any  regularity.  The  names  are  valueless,  except  as 
showing  that  the  glass  sometimes  dissolves,  and  some- 
times resists  the  effect  of  the  acid. 

Silica  44-54;  Gr.  2.5-2.7;  water  6-7. 

They  form  thin  linings  to  vesicular  cavities,  thin  crusts  on 
lava-flows,  and  seldom  occur  in  large  masses,  except  in  the 
Kilauea  lavas,  where — owing  to  the  enormous  extent  of  the 
crater — the  cooling  is  exceptional,  and  it  is  there  in  quite 


232  MANUAL   OF  LITHOLOGY. 

thick  crusts  as  pumice.  In  one  instance  it  is  a  dike  one 
inch  thick.  The  color  varies  from  grayish  white  to  black 
through  olive-green  and  greenish  black,  blue  to  bluish  black, 
or  shades  of  brown.  The  structure  is  compact ;  it  occurs 
only  in  small  pieces,  porous,  slaggy,  pumiceous,  hairlike, 
perlitic,  and  porphyritic  ;  when  the  last,  the  phenocrysts  are 
(in).  The  fracture  is  conchoidal ;  fuses  easily  to  a  slaggy 
glass ;  hardness  less  than  that  of  obsidian ;  magnetic,  and 
generally  opaque  in  the  thinnest  splinters.  Owing  to  the 
failure  to  divide  the  basalt  vitrophyres  between  tachylite 
and  hyalomelane,  Judd  and  Cole  suggest  "  basalt  glass"  for 
all  such  states. 

1.  Hydrotachylite  (Petersen).     From  Rossberg,  Darm- 
stadt.    A  somewhat  weathered  bottle-green  to  black  glass, 
with  greasy  luster,  conchoidal  fracture,  and  usually  clear 
of  phenocrysts.     Easily  soluble  in  concentrated  HC1 ;  easily 
fusible.     Silica  47.8;  Gr.  2.103;   H.   3.     This  is  a  state  of 
nepheline-basalt  which  had  silica  as  low  as  40.53  ;  Gr.  2.524; 
H.  5-6;  and  difficultly  soluble  in  concentrated  HC1. 

2.  Leucite-basanite-perlite,  Obsidian,  and  Pumice.    The 
Vesuvian  lavas  are  crusted  with  these  states.     The  glass  is 
black  and  vitreous  or  pitchy,  and  yellowish  brown  by  trans- 
mitted light,   carrying  spherules   and    phenocrysts  of  (M) 
leucite   and   augite.      Porous   white    pumice   comes    from 
Monte  Somma  and  Pompeii.     Silica  47.8 ;  Gr.  2.77.     It  is 
found  in  Italy,  Java,  Lower  California. 


PRIMARY  ROCKS.  2$$ 

LIMBURGITE   (Rosenbusch),   Magma-basalt  (Bo- 

ficky). 

A  microcrystalline  to  compact  basaltic  groundmass  carry- 
ing  usually  only  (M)  phenocrysts  of  olivine,  some- 
times  of  augite  and  hornblende,  and  composed  of  oli- 
vine, augite,  and  magnetite,  with  more  or  less  glass 
base.  As  accessories  occur  nepheline,  leucite,  and 
plagioclase. 

Silica  40-43  ;  Gr.  2.83-2.97;  water  2-5. 

A  rock,  first  found  near  Limburg,  without  a  feldspathic 
mineral,  which  occurs  like  basalt  extensively  in  Germany,. 
Bohemia,  Spain,  Cape  Verdes,  South  Africa,  Portugal, 
Brazil,  Greenland,  etc.  The  augite  is  large  and  green,  or 
small  and  light  brown  to  yellow  ;  hornblende  is  large  ;  olivine 
is  of  the  hyalosiderite  type,  with  metallic  luster  and  yel- 
lowish green  to  golden  yellow  color;  the  amount  of  glass 
varies ;  secondary  minerals  are  carbonates,  zeolites,  chal- 
cedony, and  hyalite.  There  are  two  types : 

1.  /Wdfr/tfr-magma-basalt,  where  the  rock  is  not  much 
affected  by  acids ;  is  almost  holocrystalline  with  a  small 
amount   of   brown   glass,   and   forms  hyalomelane  glass, 
analogous  to  the  basalts. 

2.  Feldspathoid  Magma-basalt,  with  abundant  clear  glass 
base  ;  gelatinizes  with  HC1  to  form  much  NaCl  on  evap- 
oration ;  forms  glass  of  the  tachylite  type,  and  is  analogous 
to  the  nepheline-basalts. 

Verite  (Osann),  Mica-magma-basalt.  From  Vera,  near 
Cabo  de  Gata,  Spain,  where  it  occurs  as  a  lava-stream.  (M) 
a  black  lava  with  pitchy  luster;  often  amygdaloidal;  carry- 
ing phenocrysts  of  brown  mica  in  folia,  visible  (M)  and 
readily  with  the  lens.  The  groundmass  is  a  glass  rich  in 
mica,  olivine,  diopside-like  pyroxene,  and  some  apatite. 
Silica  55.17. 


234  MANUAL    OF  LIT  HO  LOG  Y. 

AUGITITE  (Doelter). 

A  black  compound  of  augite,  magnetite,  and  glass  base. 
Silica  41-45. 

This  was  first  found  as  a  lava  in  the  Cape  Verdes,  and 
also  occurs  occasionally  in  Bohemia,  Venezuela,  France, 
Portugal,  Brazil,  etc.  The  glass  base  is  either  brown  or 
yellow,  and  is  soluble  in  HC1  with  slight  difficulty  ;  or  it  is 
colorless  and  readily  soluble.  Augite  rarely  forms  large 
phenocrysts,  but  is  usually  a  confused  mixture  of  small  yel- 
lowish or  reddish  prisms.  Haiiyne  is  sometimes  accessory  ; 
plagioclase,  nepheline,  biotite,  hornblende,  apatite,  specular 
hematite,  ind  magnetite  occur.  It  readily  forms  zeolites. 

1.  Haiiynetachylite  (Mohl),  is  a  brown  glass  from  the  South 
Sea  Islands,  carrying  the  above,  and  is  a  glassy  augitite. 

2.  Ehrwaldite  (Cathrein).     A   greenish  to  grayish-black 
microcrystalline  groundmass  with  black  lustrous  augite  f  to 
i  J  inches  ;  brown  biotite  to  f  inch  ;  brownish  to  dark-green 
phenocrysts  of  bronzite  turned  to  bastite.      The  ground- 
mass  (m)  is  doleritic,  and  carries  much  basaltic  hornblende, 
augite,  rhombic  pyroxene,  biotite,  apatite,  and  magnetite. 
It  weathers  to  carbonates  and  zeolites.     There  is  neither 
olivine  nor  nepheline. 

GROUP   22.     GABBROS. 

Ilia.  BASALT-GABBRO  INTRUSIVES. 

(Necessary  minerals  :  Plagioclase,  olivine,  pyroxene,  magnetite.) 

These  may  be  arranged  according  to  the  predominant 
mineral : 

1.  Plagioclase  series,  Gabbros. 

2.  Olivine  series,  Peridotites. 

3.  Pyroxene  series,  Pyroxenites. 

4.  Magnetite  series,  Magnetites. 


PRIMARY  ROCKS.  335 

GABBROS. 

Combinations,  varying  from  coarse  granitoid  to  compact,  of  predom- 
inant plagioclase,  a  pyroxene,  olivine,  and  magnetite  in  varying  propor- 
tions. They  can  be  divided,  according  to  the  size  of  their  crystals,  and 
their  predominant  mineral,  into  : 

I.  GRANITOID  GABBROS  : 

a.  Plagioclase  and  diallage,  Gabbro  ;  with  olivine,  <9//-z//>z<?-gabbro. 

b.  Plagioclase  and  rhombic  pyroxene,  Norite  ;  with  olivine,  OK- 


c.  Plagioclase,  Anorthosites  ;  with  olivine,  Troctolite 

II.  GRANULITIC  GABBROS  : 

a.  Plagioclase  and  augite,  Diabase  ;  with  olivine, 

III.  GABBRO-PORPHYRITES  : 

a.  Plagioclase  and  rhombic  pyroxene,  ./V0r//<?-porphyrite. 

b.  Plagioclase  and  augite,  Dzafrase-porphyrite. 

c.  Plagioclase,  Labrador  porphyrite. 

d.  Augite,  ^4z^7/<?-porphyrite. 

IV.  MlCROCRYSTALLINE  GABBROS  I 

a.  Without  olivine,  Aphanite. 

b.  With  olivine,  Melaphyre. 

V.  GABBRO  GLASS: 

a.  Gabbro  glass. 

b.  Diabase  glass. 

c.  Variolite. 

\a.    GABBRO  (Breislak),  Diallagite  (Descloiseaux), 

Granitone. 

A  holocrystalline,  granitoid,  equidimensional  mixture  of 
plagioclase  and  diallage,  with  magnetite,  titanite, 
apatite,  and  olivine. 

Silica  43-54  ;  Gr.  2.8-3.2. 

It  occurs  as  masses,  bosses,  intrusive  sheets,  dikes,  and 
•surface  sheets  in  Saxony,  Silesia,  the  Harz,  the  Rhone  dis- 
trict, Bohemia,  the  Alps,  Italy,  Spain,  France,  Great  Britain, 
Norway,  Sweden,  Iceland,  Japan,  Africa,  Australia,  South 
America,  Massachusetts,  New  Hampshire,  Delaware,  Mary- 


236  MANUAL    OF  LITHOLOGY. 

land,  New  York,  Colorado,  about  Lake  Superior,  California, 
The  typical  gabbro  is  very  coarse-grained  and  granitoid, 
with  predominant  plagioclase.  It  also  has  fine-grained  tex- 
tures, seldom  amorphous,  and  exhibits  parallel  (banded,, 
striped,  schistoid),  fluidal  and  somewhat  centric  structures. 
Plagioclase  is  labradorite  or  anorthite  (sometimes  oligoclase, 
and  even  orthoclase  with  quartz),  and  is  usually  in  isometric 
crystalline  grains  (sometimes  two  inches)  of  a  grayish  white 
color  (sometimes  brownish  and  bluish  violet).  The  feldspars 
sometimes  change  to  saussurite,  as  stated  under  the  minerals, 
though  it  is  also  a  compact  zoisite  or  a  form  of  garnet. 
Diallage  is  bladed,  in  irregular  tables  or  in  grains,  colored 
gray,  brown,  oil-green,  with  strong  metallic-pearly  luster. 
The  plates  are  sometimes  three  inches  broad.  It  alters  to 
grass-green  smaragdite  with  pearly  luster.  Judd  thinks 
diallage  only  a  "  schillered  "  augite,  and  the  augite  and 
rhombic  pyroxene  (enstatite)  the  primary  forms  of  the 
group.  Hornblende,  rhombic  pyroxene,  and  mica  are  fre- 
quent essentials  and  ( M) ;  as  accessories  are  garnet,  zircon 
(sometimes  one  inch  long),  pyrrhotite  (not  pyrite),  and 
secondary  calcite.  The  minerals  crystallized  at  the  same 
time  and  are  generally  hypidiomorphic.  Olivine  occurs 
(M)  and  is  sometimes  very  abundant.  It  usually  alters  to 
other  minerals  (serpentine  and  chrysotile).  The  rock  is 
usually  poor  in  accessories.  With  predominant  hornblende 
the  rock  is  diorite  ;  with  rhombic  pyroxene,  a  norite  ;  with 
augite,  a  diabase.  It  cannot  be  traced  into  hypocrystalline 
nor  porphyritic  varieties,  nor  is  it  accompanied  by  tuffs. 

i.  Zobtenite  (J.  Roth).  From  the  Zobtenberg,  Silesia.  A 
schistoid  gabbro,  which  also  has  an  olivine  variety.  A  coarse- 
to  fine-grained  rock,  also  found  on  the  selvages  of  gabbro 
eruptions,  as  is  usually  the  case  with  mixtures  of  highly 
unequiaxial  black  minerals,  and  with  parallel  arrangement 
to  the  dike-walls. 


PRIMARY  ROCKS,  237 

2.  Beerbachite  (Chelius).      A   fine-granular   dike-gabbro 
which  also  carries  olivine,  from  the  Melibocus,  with  silica 
47.     Hornblende  sometimes  replaces  diallage. 

3.  Odinite  (Chelius).    From  near  Darmstadt  in  a  dike,  with 
silica   52.      A  gray  groundmass  carrying  plagioclase   and 
green  to  colorless  augite  with   mica  in  the  center  of  the 
dikes,  which  are  coarse-grained  there. 

Hypersthene-gabbro,  Gabbro-granite  (Chester).  From 
Delaware,  where  it  contains  accessory  quartz,  basaltic  horn- 
blende, and  biotite.  Hypersthene-gabbros  also  occur  in 
the  Odenwald,  at  Monzoni,  etc. 

Hornblende-gabbro  (Chelius).  From  the  Odenwald, 
Black  Forest,  Alsace,  etc.,  with  scanty  diallage  and  abun- 
dant hornblende  (J  to  2  inches).  This  is  like  diorite.  In 
some  of  the  localities  the  diallage  has  altered  to  hornblende 
by  paramorphism. 

i.  Smaragdite-gabbro,  with  diallage  altered  to  smarag- 
dite,  with  grass-green  color  and  pearly  luster,  and  plagio- 
clases  not  much  changed  to  saussurite.  At  Mittleberg,  etc. 

(Some  authorities  place  here  the  alteration  products 
from  diallage  to  hornblende,  as  the  so-called  "  hyperite-dio- 
rites,"  etc.  These  have  been  described  under  "  Diorite.") 

Mica-gabbro.  From  the  Brocken,  Harz.  A  fine-grained 
rock  rich  in  biotite  and  augite  and  poor  in  olivine.  Quartz 
appears  more  frequently  than  in  normal  gabbro,  as  would 
be  the  case  with  micaceous  rocks.  It  is  found  elsewhere 
as  a  variety  in  gabbro  formations. 

Orthoclase-gabbro  (Irving).  From  Lake  Superior,  with 
orthoclase,  oligoclase,  apatite,  diallage,  and  much  basaltic 
hornblende.  It  is  generally  free  from  olivine  and  carries 
secondary  quartz. 

Saussurite-gabbro,  Euphotide  (Haiiy).  A  rock  from 
Italy,  France,  Sweden,  etc.,  where  plagioclase  is  altered  to 


238  MANUAL   OF  LITHOLOGY. 

saussurite  and  diallage  to  smaragdite,  with  titanite,  chro- 
mite,  pyrite,  serpentine,  and  carbonates.  Silica  43-50  ;  Gr. 
2.65-3.69  ;  H.  2.5-3  I  fusibility  3-3.5,  and  more  or  less  at- 
tacked by  acids.  The  euphotide  of  Mont  Rosa  has  Gr.  3.65  ; 
from  Sweden,  3.60 ;  from  France,  2.69.  As  they  have  their 
diallage  more  or  less  changed,  they  are  classed  as  saussurite- 
diallage-gabbro  and  saussurite-smaragdite-gabbro. 

Olivine-gabbro  (G.  Rose).  A  gabbro  containing  (M) 
olivine  in  small  blackish  green  grains,  or  its  weathered 
equivalent  (serpentine  or  chrysotile).  It  occurs  in  Scandi- 
navia, Great  Britain,  Japan,  Waterville  and  Mount  Washing- 
ton, N.  H.,  Cortlandt,  N.  Y.,  Maryland,  Minnesota,  Iron 
Mountain,  Col,  St.  John,  N.  B. 

i.  Olivine-enstatite-gMoro.  From  the  Western  Isles  of 
Scotland,  carrying  olivine  and  enstatite. 

U.  NORITE  (Esmark). 

A  usually  coarse-  to  fine-grained  (sometimes  granitoid, 
porphyritic,  and  ophitic)  compound  of  plagioclase 
and  a  rhombic  pyroxene  (hypersthene,  enstatite, 
bronzite),  with  diallage,  hornblende,  orthoclase,  il- 
menite,  and  magnetite,  also  olivine  and  quartz. 
Silica  43-65;  Gr.  2.8-3.1. 

It  occurs  in  widely  extended  masses  in  Laurentian  for- 
mations— especially  in  Scandinavia  and  North  America ; 
also  in  dikes.  It  is  found  in  New  York,  Pennsylvania,, 
Delaware,  Maryland,  North  Carolina.  It  is  associated  with 
beds  of  titaniferous  magnetite,  and  some  authorities  see  in 
this  a  segregation  from  a  gabbroitic  magma.  The  minerals 
appear  as  in  gabbro,  and  orthoclase  is  sometimes  two  inches 
long.  The  typical  norite  has  a  highly  basic  plagioclase 
with  enstatite  or  hypersthene,  and  with  little  diallage,  horn- 
blende, or  biotite.  A  high  percentage  of  quartz  forms 


PRIMARY  RGCKS.  239 

quartz-norite,  and  of  olivine,  olivine-uorite.  A  quartz-norite 
from  Mount  Hope,  Md.,  carries  orthoclase  and  blue  quartz. 

Hypersthene-norite,  when  hypersthene  is  the  predomi- 
nant mineral.  This  is  found  about  Lake  Superior,  the 
Adirondacks,  in  Delaware,  etc.  Some  authorities  call  this 
"hyperite,"  while  others  use  that  term  for  "augite-norite." 
This  is  a  misnomer,  as  it  is  only  a  norite. 

Monzonite.  A  variety  of  the  above  from  Monzoni  in 
the  Tyrol.  Name  no  longer  used. 

Bronzite-norite.  A  variety  with  bronzite,  now  em- 
braced under  the  general  term.  From  Finland. 

Augite-norite.  A  compound  of  hypersthene,  augite, 
biotite,  reddish  brown  feldspar,  fibrous  diallage,  with  the 
first  two  equally  prominent.  Cortlandt,  N.  Y.  Silica  55. 

Mica-norite.  A  compound  of  magnetite,  hypersthene, 
biotite  (bent  and  twisted  about  large  portions  of  feldspar), 
broken  and  bent  plagioclase,  and  garnet.  Schistoid  by 
selvage  action  at  Cortlandt,  N.  Y. 

Hornblende-norite.  A  transition  between  norite  and 
diorite.  From  the  Alps. 

Spheroidal  Norite,  Ball  Gabbro,  "  Potato-stone."  From 
Romsas,  with  thick-shelled  greenish  brown  concretions  (up 
to  six  inches  diameter)  of  biotite  flakes  and  hypersthene,  in  a 
light-colored  ground  mass  of  labradorite,  oligoclase,  biotite, 
and  magnetite  ;  also  at  Cortlandt,  N.  Y. 

Ic.  ANORTHOSITE  (F.  D.  Adams). 
A  gabbro  with  predominant  feldspar  (anorthite)  to  the 
almost  entire  exclusion  of  all  other  ingredients. 

The  plagioclase  is  frequently  95  per  cent  of  the  rock,  and 
none  of  the  essentials  or  accessories  are  ever  abundant,  such 
as  hyperite,  augite,  hornblende,  biotite,  titanite,  and  magne- 
tite. It  occurs  extensively  in  the  Laurentian  of  New  York, 
Canada,  about  Lake  Superior,  Labrador,  and  Newfoundland. 


240  MANUAL   OF  LITHOLOG  F. 

1.  Forellenstein,  Troctolite  (Bonney).      A   gabbro   com- 
posed of  olivine  and  plagioclase.     The  olivine  is  altered  to 
serpentine.    There  is  little  or  no  diallage.    From  the  vicinity 
of  Neurode,  where  it  has  the  local  name  given  above ;    but 
the  contrast  of  the  spots  of  blackish  green  serpentine  grains 
against  the  snow-white  feldspar  led   Bonney  to  call  it  as 
above  given  from  its  resemblance  to  the  sides  of  a  trout. 
The  plagioclase  is  always  like  anorthite.    Silica  41.13;  Gr. 
2.88.     Found  in  Canada. 

2.  Ossipyt  (Hitchcock)  is  a  similar  rock  from  Ossipee, 
N.  H.,  with  labradorite,  olivine,  magnetite,  and  an  amphibole. 

(This  series  is  the  "  complement "  of  magnetite  in  the 
differentiation  of  a  gabbroitic  magma.) 

GRANULAR   GABBRO. 

\\a.  DIABASE  (Haussmann). 

A  coarse-  to  fine-grained  and  usually  compact  and  ophitic 
greenish  compound  of  plagioclase,  augite,  and  gener- 
ally viridite,  with  specks  of  ores  and  accessory  bio- 
tite,  rhombic  pyroxene  (usually  (m)\  olivine  as  in 
gabbro  ;  quartz  occasionally  (m). 

Silica  43-56;  quartz-diabase  53-58;  Gr.  2.8-3. 

It  occurs  as  surface  and  intrusive  sheets  and  beds,  and  as 
dikes,  and  joints  and  weathers  like  basalt.  A  locality  on  the 
shore  of  Lake  Superior  in  a  width  of  14  inches  exhibits  28 
intrusions  of  diabase  into  granite  ;  so  that  27  granite  plates, 
varying  in  thickness  from  J  inch  to  8  inches,  lie  between 
them.  It  is  abundantly  developed  throughout  the  world, 
and  especially  in  the  Trias  of  the  Atlantic  border  of  the 
United  States.  It  is  usually  fine-grained  and  frequently 
aphanitic  and  porphyritic ;  also  schistose ;  parallel  struc- 
tures; variolitic,  and  amygdaloidal.  The  cavities  of  the  rock 
in  the  last  state  are  filled  with  quartz,  actinolite,  asbestus, 


PRIMARY  ROCKS.  24! 

pistacite,  cat's-eye,  axinite,  calcite,  dolomite,  native  copper, 
and  zeolites.  The  diabase-/w/ hy rites  are  in  small  dikes  or 
the  selvages  of  great  ones.  It  also  shows  tuffs.  Olivine  is 
variable.  Plagioclase  is  oligoclase,  labradorite,  bytownite, 
and  anorthite  ;  tabular,  lath-shaped,  and  regular ;  white, 
grayish  white,  and  greenish  white.  Augite  is  brownish  to 
brownish  black  as  idiomorphs,  irregular  grains,  and  slender 
laths ;  quartz  and  orthoclase  are  (m) ;  biotite  is  usually  in 
the  hornblendic  varieties  of  coarse  grain.  Augite  alters  to 
chlorite,  serpentine,  and  uralite.  Viridite  occasionally  is  in 
(M)  folia.  It  colors  the  rock.  Epidote  is  also  a  secondary 
product.  The  color  is  usually  green.  The  Washoe  diabase 
is  blue  when  freshly  blasted  ;  in  a  minute  it  shows  brownish 
shades,  and  in  five  minutes  it  is  entirely  brown.  When  in 
dikes  and  masses,  diabase  is  frequently  altered  to  schists  by 
squeezing.  Barus  fused  a  diabase  with  Gr.  3.0178  to  a  glass 
with  Gr.  2.717,  and  argues  that  the  original  density  is  due 
to  pressure  during  solidification. 

1.  Leucophyre  (Gumbel).     From  the  Fichtelgebirge.     A 
light-colored  saussurite-like  rock  with  green  augite,  colored 
by  viridite,  and  carrying  titanite,  plagioclase,  piedmontite, 
augite  (either  green  or  brown),  scanty  hornblende.    Silica  71. 

2.  Proterobase  (Gumbel).     From  the  same  locality,  and 
meaning  an  older  rock  than  the  others.     It  carries  primary 
basaltic  hornblende.     A  later  rock  is  called  hysterobase. 

3.  Algovite  (Reiser).     A  granular  to  compact  dark-green 
to  reddish  brown  amygdaloidal  and  porphyritic  rock  with 
great  plagioclases.     The  only  (M)  minerals  are  plagioclase 
and  light-brown  augite. 

4.  Diabase-pegmatite  (Brogger).     From  Brandbokampus, 
Norway,  and  composed  of  augite,  basaltic  hornblende,  and 
titanite  in  large  grains,  with  very  basic  plagioclase,  in  dikes 
where  large  crystals  are  formed  like  pegmatite,  of  plagio- 
clase with  hornblende  and  augite  playing  the  role  of  quartz. 


242  MANUAL   OF  LITHOLOGY. 

5.  Calcareous  Diabase.  This  is  no  longer  known  as  a 
separate  rock,  as  the  calcite,  in  any  case,  is  a  secondary 
product.  There  were  states  of  this  called  calcareous  apha- 
nite  and  schalstein. 

Sahlite-diabase  (Tornebohm).  From  Sweden,  England. 
Idiomorphic  diopside-like  augite  with  frequent  quartz. 
Also  in  the  Trias  sandstone  of  the  Connecticut  Valley. 

Enstatite  (Bronzite)-diabase  (Rosenbusch).  From  Saar- 
Nahe  district,  Sweden,  England.  A  hypersthene-diabase  is. 
found  in  New  Jersey,  Virginia,  etc. 

Uralite-diabase.  From  the  Schwarzwald,  Harz,  Cyprus, 
Sweden,  the  iron  region  of  Michigan.  This  is  distinct  from 
hornblendic  proterobase.  A  medium-grained  compound  of 
bytownite,  large  fibrous  prisms  of  uralitized  pyroxene,  com- 
pact grains  of  hornblende,  and  biotite.  It  alters  to  epidote 
and  chlorite.  It  is  widely  scattered  throughout  the  world,, 
with  diabase,  but  of  limited  occurrence  at  any  one  place.  It 
is  accompanied  by  garnet  in  Michigan. 

Mica-diabase  (Emerson).  In  dikes  at  Franklin,  N.  J.  It 
is  spherulitic,  with  small  pyroclasts  of  fused  willemite  from 
the  dike-walls  through  which  it  broke.  It  is  composed  of 
labradorite,  augite,  biotite,  apatite,  and  titanite. 

Ophite  (Palassou).  From  the  Pyrenees,  Spain,  Portugal. 
A  coarse-grained  to  (M)  dense  and  seldom  porphyritic  rock, 
light- and  dark-green  to  black.  Gr.  2.7-3;  silica  49.50.  It 
occurs  as  dome-shaped  masses  and  dikes.  It  is  a  uralitized  dia- 
base with  columnar  jointing  and  spheroidal  weathering,  so- 
that  concentric  shells  can  be  removed  as  in  the  case  of  basalt. 
(M)  plagioclase  and  augite  are  not  abundant ;  secondary 
calcite  occurs  in  veins,  and  some  kinds  effervesce  with  acids. 

Teschenite  (Hohenegger).  In  irregular  masses,  apophy- 
ses,  and  dikes.  From  eastern  Silesia.  A  felsitic  rock  with 


PRIMARY  ROCKS.  243 

intersertal  texture  in  which  hornblende  forms  long  black 
acicular  crystals  of  basaltic  type  ;  apatite  the  same  at  times. 
Named  from  Austrian  Silesia  (Teschen).  Plagioclase  is  lab- 
radorite-bytownite-anorthite  ;  augite  (M)\  ilmenite;  scanty 
biotite.  When  coarse-grained,  hornblende  and  augite  are  in 
(M)  individuals.  Analcite  is  abundant,  and  on  this  account 
Rosenbusch  places  this  with  theralite,  as  another  combina- 
tion of  plagioclase-feldspathoid  rock;  but  Zirkel  states  that 
the  microscope  shows  that  the  last  mineral  is  formed  at  the 
expense  of  labradorite,  and  not  from  a  possible  nepheline  or 
leucite.  It  occurs  (M).  Chlorite  and  calcite  are  secondary. 

Olivine-diabase.  Silica  48.18  ;  Gr.  2.93-3.19.  It  occurs  in 
dikes  in  Germany,  Sweden,  Great  Britain,  Asia,  South 
Africa,  Brazil,  in  the  United  States  in  Minnesota,  Deerfield, 
Mass.,  Campton,  N.  H.,  Kennebunkport,  Me.,  Orange,  N.  J., 
Nevada.  Olivine  is  partly  fresh  and  partly  opalized  and 
serpentinized ;  augite  is  partly  like  diallage ;  hornblende  and 
biotite  are  (M)  in  the  coarse-grained  states  to  a  higher 
degree  than  in  diabase ;  and  much  hornblende  forms  olivine- 
proterobase.  Plagioclase  is  usually  labradorite ;  anorthite 
forms  the  variety  eukrite  (with  little  olivine  and  biotite,  but 
much  magnetite);  orthoclase  is  found  in  large  Carlsbad  twins 
at  Falkenstein,  Saxony  (two  inches  long).  The  texture 
varies  from  granitoid  to  ophitic,  compact,  vesicular,  and 
slaggy  ;  in  beds,  extrusive  and  intrusive  sheets,  and  dikes. 

PORPHYRITES   OF   THE   GABBRO   GROUP. 

Ilia.  NORITE-porphyrite. 

A  half-glassy  rock  with  porphyritic  structure ;  pitchy 
luster ;  carrying  small  phenocrysts  of  rhombic 
pyroxene  and  (M)  plagioclase ;  without  quartz,  horn- 
blende, or  biotite. 

Silica  56-60 ;  Gr.  2.7-3. 

A  scarce  rock,  associated  with  norite,  and  only  possible 


244  MANUAL    OF  LITHOLOG  Y. 

where  rhombic  pyroxene  is  abundant.  It  is  called  enstatite- 
porphyrite,  ^>'/m/^-porphyrite,  etc.,  as  the  pyroxenic 
mineral  changes,  and  0/zV/W-norite-porphyrite,  when  olivine 
also  appears  as  phenocrysts. 

Hyper sthene-quartz-Tpor^\\y  rite  (Lossen).  From  Elbin- 
gerode,  as  a  hornstone-like  groundmass  with  (M)  pheno- 
crysts of  plagioclase,  hypersthene,  small  quartzes,  and 
sporadic  garnet ;  orthoclase  is  (m) ;  also  biotite,  apatite,  and 
zircon.  Silica  69.94. 

lllb.  DIABASE-porphyrite  (Rosenbusch). 
A  holocrystalline  groundmass  (///),  carrying  (M)  pheno- 
crysts of  labradorite  and  augite. 
Silica  43-58  ;  Gr.  2.9. 

The  following  porphyrites  occur  in  dikes,  as  selvages  to 
diabases,  in  Saxony,  Thuringian  Forest,  Harz,  Nassau,  Saar- 
Nahe  district,  Vosges,  Greece,  Bulgaria,  Switzerland,  Italy, 
Great  Britain,  Sweden,  Asia,  Egypt,  Victoria,  in  United 
States  about  Lake  Superior.  They  joint  and  weather  like 
diabase  and  basalt.  Plagioclase  is  white  to  greenish  white, 
usually  J  inch  long  (rarely  i £  inches),  and  generally  altered 
and  stained  with  chlorite  and  epidote;  augite  is  in  stout 
prisms,  greenish,  greenish  brown,  and  black,  and  pitch-black 
(all  in  the  same  fragment) ;  quartz  (;«).  The  groundmass  is 
greenish  gray  to  blackish  green ;  seldom  brownish  black  or 
reddish  violet;  when  fresh  gives  the  microcrystalline 
glimmer;  sometimes  there  is  a  small  amount  of  (m)  glass 
base ;  drusy,  amygdaloidal  (filled  with  calcite,  quartz, 
chalcedony,  cat's-eye,  epidote,  axinite,  and  zeolites). 

Black  Porphyry  (Streng).  From  Elbingerode,  Harz, 
with  a  black  groundmass  carrying  (M)  phenocrysts  of  labra- 
dorite and  small  prisms  of  augite,  with  accessory  mica  in 
brownish  black  folia,  pyrite,  and  magnetite.  The  ground- 
mass  is  seen  to  be  crystalline  by  the  lens. 


PRIMARY  ROCKS.  24$ 

lllc.  LABRADOR  Porphyrite  (Delesse). 
A  compact  grayish  green,  dark-green,  even  reddish-violet 
ground  mass,  with  phenocrysts  of  greenish  labradorite 
in  tables  from  one-third  to  two-thirds  of  an  inch  long, 
and  rarely  small  augites. 

Silica  54 ;  Gr.  2.77  ;  water  2.5. 

The  general  occurrence  and  character  are  as  described 
under  "  Diabase-porphyrite."  It  is  found  at  Duluth,  Wis., 
and  Taylor's  Falls,  Minn.  The  varieties  are  : 

1.  Cuselite  (Rosenbusch),  with  bluish  gray  groundmass 
carrying  -J  inch  plagioclase  and  chloride  grains.    Silica  58.02. 

2.  Porfido-verde-antico.     From     Laconia,   Greece,    Great 
Britain,  etc.     An  olive-green   groundmass  which  becomes 
lighter  on  heating,  carrying  dark-green  augite  and  greenish 
white  labradorite  phenocrysts.     Silica  53  ;  Gr.  2.91.      Epi- 
dote,  chlorite,  and  quartz  are  secondary. 

\\\d.  AUGITE-porphyrite. 

A  compact  dark-green  matrix  carrying  phenocrysts  of 
augite  of  £  inch  and  over. 
Silica  42-49  ;  Gr.  2.9. 

Abundant  as  dikes  and  lava-streams  in  the  Alps,  with 
vesicular  and  amygdaloidal  states  common.  There  are 
placed  as  varieties  : 

1.  Uratite-porphyry  (G.  Rose).     First  described  from  the 
Urals,  with  a  dense  greenish  gray  groundmass  (sometimes 
blackish  gray  carrying  phenocrysts  of  plagioclase  from  i  to 
i|  inch,  and  uralite).     Silica  61  ;  Gr.  3. 

2.  3/z^-augite-porphyrite.      From  England,  with   abun- 
dant folia  of  mica  and  augite.     Silica  48-51  ;  Gr.  2.57. 


246  MANUAL    OF  LITHOLOGY. 

MICROCRYSTALLINE    GABBROS. 

I Va.  APHANITE  ("  Unresolvable  "). 
This  is  a  compact  state  of  the  gabbro  group,  and  in  hand 
specimens  can  only  be  divided  into  the  diabase  and  other 
forms  by  the  presence  of  a  few  phenocrysts,  which  are  not 
sufficiently  important  to  form  a  porphyrite.  It  may  be 
taken  as  the  groundmass  of  the  porphyrites,  and  varies  from 
microcrystalline  to  compact  (m),  but  with  small  amount  of 
glass  base.  When  it  becomes  glassy,  it  falls  under  the  next 
division  of  the  group.  We  can  distinguish  only  norite  and 
diabase-aphanites,  as  gabbro  cannot  yet  be  reported  in  com- 
pact or  porphyritic  states,  and  norite  rarely. 

I.  Norite-aphanite  is  reported  from  Fifeshire,  Scot- 
land. A  compact  grayish-black  rock  associated  with 
norite  there. 

II.  Diabase-aphanite. 

A  (M)  compact  diabase  without  phenocrysts,  forming 
an  apparently  homogeneous  mass,  dark  green  to  black, 
as  hard  as  feldspar  ;  dull  luster,  subconchoidal  frac- 
ture;  sometimes  slightly  porphyritic,  vesicular, 
amygdaloidal,  and  slaty. 
Silica  43-58  ;  Gr.  2.6-3. 

This  is  associated  with  diabase  ;  joints  and  weathers  like 
basalt.  Phenocrysts  of  augite  or  plagioclase  in  predomi- 
nance form  those  varieties  of  porphyrite.  It  bears  to 
diabase  the  relation  that  felsite  does  to  granite.  Some  au- 
thorities see  in  this  a  highly  devitrified  diabase  glass. 

j.  Calcareous  Aphanite,  Kalkaphanit.  An  aphanitic  mass 
carrying  abundant  spherules  of  calcite,  which  are  not  the 
fillings  of  amygdules. 

.  2.  Amygdaloidal  Aphanite,  Spilite,  where  the  calcite, 
quartz,  or  other  minerals  are  the  filling  of  amygdules.  The 
French  geologists  call  this  spilite. 


PRIMARY  ROCKS.  247 

(NOTE  on  diabase  rocks.  Many  geologists  make  no  dis- 
tinction between  diabase  and  dolerite,  other  than  that  of 
color  and  difference  in  age.  They  both  contain  the  same 
mixtures  and  appear  in  the  same  states.  The  color  is  said 
to  be  due  to  the  formation  of  viridite,  and  the  greater  abun- 
dance in  amygdaloidal  states  in  diabase  is  due  to  greater  age 
and  exposure  to  metachemic  agents.  Others  note  that  there 
are  diabases  without  viridite,  which  seem  to  be  older  forms 
of  augite-andesite.  There  is  also  a  difference  in  texture  in 
•diabase  and  dolerite,  which  may  be  due  to  longer  exposure 
to  the  above-named  agencies.  At  any  rate,  both  are  placed 
in  the  group  of  gabbros,  and  are  most  intimately  associated.) 

IVb.  MELAPHYRE  (Brongniart). 

A  compact  half-pitchy  black,  green,  red,  brown,  bluish 
purple  groundmass,  weathering  to  brown,  red,  and 
green,  composed  of  (m)  plagioclase,  pyroxene,  and 
olivine,  and  carrying  at  times  phenocrysts,  which  are 
usually  olivine  (sometimes  ^  inch,  and  usually  visible 
with  a  lens).  It  is  associated  in  Scotland  with  augite- 
andesites,  and  is  thought  by  some  to  be  an  olivine 
variation  of  them  ;  by  the  majority  of  petrographers, 
as  an  oiivine  variation  of  basalt  and  aphanite. 
Silica  51-57;  Gr.  2.68-2.85. 

It  occurs  in  beds,  sheets,  dikes,  bosses,  and  pyramidal 
masses  in  Silesia,  Thuringian  Forest,  Saxony,  Bohemia,  Great 
Britain,  France,  Hungary,  the  Alps,  Spain,  Greece,  South 
Africa ;  in  the  United  States  at  Keweenaw  Point,  Lake 
Superior,  Nevada,  Kennebunkport,  Me.  It  joints  irregularly 
in  columns,  tables,  etc.,  and  when  weathered  is  full  of 
ferrite,  epidote,  calcite,  etc.  A  number  of  varieties  are 
made  on  (m)  variations  of  groundmass. 

With  this  rock,  when  amygdaloidal,  are  associated  native 
copper  (Lake  Superior),  silver  (the  same),  zinc  ores,  jasper, 


248  MANUAL   OF  LITHOLOGY. 

chalcedony,   agate,  amethyst,   calcite,   etc.,   in  abundance, 
never  with  zeolites,  so  that  the  Oberstein  rock  was  worked 
for  agate  till  exhausted.     Epidosite  is  an  epidotized  variety. 
Navite  (Rosenbusch)   is   a   red  groundmass  carrying 
phenocrysts    of    plagioclase   and   olivine.      From   Ober- 
stein. 

V.   GABBRO    GLASS. 

With  the  exception  of  diabase,  these  are  not  very  abun- 
dant, as  the  rocks  are  very  basic  and  do  not  easily  form  such 
states,  as  their  low  heat  content,  in  proportion  to  their  great 
fluidity,  allows  them  to  form  stony  states  under  conditions 
where  the  acid  rocks  would  only  form  glasses.  The  occur- 
rence of  gabbro  is  given  as  a  probable  gabbro  glass.  No 
norite-glass  is  reported  as  yet. 

(a)  Gabbro  Glass.  From  Carrock  Fell,  England,  in  a  dike 
one  inch  thick,  traversing  gabbro,  and  reported  as  probably 
part  of  it,  as  shown  by  its  high  specific  gravity  (2.99).  A 
greenish  to  purplish  glass,  weathering  yellowish  brown ; 
waxy  luster  ;  slightly  magnetic  ;  H.  6.5  ;  silica  51-53  ;  fuses  to 
a  black  enamel  on  thin  splinters. 

(ft)  Diabase  Glass.  In  some  cases  this  is  simply  the  ex- 
tension of  the  glass  base  that  is  found  in  some  diabases ;  in 
others  it  is  a  regular  glass,  with  greasy  luster,  occurring  with 
diabase,  and  forming  pitchstone,  pitchstone-porphyry,  and 
obsidian  states.  Silica  44-55  ;  Gr.  2.4-2.6.  Near  Quotshau- 
sen  the  diabase  stream  (extrusive)  is  fresh  and  has  a  glass 
crust  with  phenocrysts  of  altered  olivine.  It  is  also  found 
on  the  selvages  of  dikes  in  Scotland,  and  in  one  or  two  in 
stances  in  America;  also  in  Sweden  (see  below). 

i.  Wichtisite  (Tornebohm).  From  Finland,  in  consider- 
able masses  ;  black ;  slight  luster ;  conchoidal  fracture ; 
hardness  6.5  ;  Gr.  3.03  ;  fusible  to  a  black  enamel ;  silica 
54-56 ;  in  a  dike  4-5  inches  wide  at  Wichtis. 


PRIMARY  ROCKS.  249 

2.  Sordawalite  (Tornebohm).  From  Sordawala,  in  inch 
selvages  to  a  narrow  dike  in  hornblende-schists.  It  is 
black,  like  anthracite  ;  vitreo-greasy  luster.  H.  4-4.5  ;  Gr. 
2.55-2.62 ;  silica  47-49. 

(c)  Variolite,  Jadeglanduleux  (Brongniart).  A  light-  to 
dark-green  devitrified  spherulitic  gabbro  glass,  with  silica 
52.79 ;  Gr.  2.896.  Found  in  England,  Ireland,  Sweden,  Silesia, 
Siberia,  France,  Thuringian  Forest,  Fichtelgebirge,  Italy. 
Weathers  and  joints  spheroidally;  carries  abundant  greenish 
white  to  violet-gray  spherules  with  radial-fibrous  and  con- 
centric-shelly structure  of  a  silicate  which  are  so  firmly 
intergrown  in  the  mass  that  they  do  not  separate  on  weather- 
ing, but,  being  more  resistant  than  the  groundmass,  are  left 
projecting  above  the  surface  as  brown  pustules  (whence  the 
name).  Cole  and  Gregory  on  studying  the  occurrence  at 
Mount  Genevre  decided  that  the  rock  was  a  devitrified 
tachylite  with  spherules.  This  rock  must  not  be  confused 
with  amygdaloidal  forms  of  aphanite,  where  the  spherules 
are  calcite ;  nor  with  the  amygdaloidal  forms  of  melaphyre, 
where  they  are  silica. 

BASALT-GABBRO    INTRUSIVES. 

II.   O LI  VINE  SERIES. 
(Necessary  mineral  :  Olivine.) 

PERIDOTITE  (Rosenbusch). 

These  massive  holocrystalline  rocks  are  plagioclaseless 
gabbros  with  predominant  olivine.  Silica  26-45.  Zirkel 
objects  to  the  name  "  peridotite,"  as  in  some  cases  the  min- 
eral is  not  olivine,  but  one  of  its  varieties ;  but  the  term  is 
in  general  use,  and  is  understood  as  a  series  with  an  olivine 
mineral  predominant.  According  to  the  other  component 
or  components,  the  rocks  are  called  : 


250  MANUAL   OF  LITHOLOGY. 

(a)  Dunite  (v.  Hochstetter).     An  olivine  rock,  generally 
with  chromite.    From  Dun  Mountain,  New  Zealand.    An  al- 
most pure  aggregate  of  olivine  of  characteristic  color,  angu- 
lar   grains,    splintery   fracture,   and    vitreo-greasy   luster. 
Silica  42-43;    Gr.  3-3.3.     This  is  also  found  in  Japan,  the 
Western  Isles  of  Scotland,  and  in  a  dike  near  Willard,  Ky., 
with  abundant  garnet.     It  serpentinizes. 

(b)  Picrite   (Tschermak).     A  compound  of  olivine  and 
augite,  named  from  the  abundance  of  magnesia  ("  bitter  ") 
salt  in  it  (Greek  pikros).      In  dikes  and  beds  in  Austria, 
England,  Scotland  ;  in  United  States  in  Arkansas  (Murfrees- 
borough),  Deer  Island,  Maine,  Cortlandt,  N.  Y.    In  England 
it  is  reported  as  passing  into  diorite.    It  is  mainly  of  olivine, 
and  the  rest  a  compound  of  augite,  hornblende,  and  mag- 
netite ;  blackish  green  in  many  cases,  and  almost  compact 
with   olivine   in   phenocrysts    half  an  inch    long.      Olivine 
serpentinizes,  as  usual,  in  many  cases.    Silica  38.9 ;  Gr.  2.96. 
It  forms  porphyritic  states.     Kimberlite  (Carvall-Lewis)  is  a 
similar  rock  from  Kimberly,  South  Africa,  at  the  diamond 
mines ;  and  palceopicrite  (Gumbel)  ("  old  picrite  ")  is  a  serpen- 
tinized  form  with  abundant  chlorite  in  the  Fichtelgebirge. 

(c)  Eulysite  (Erdmann).     A  probably  metamorphic  com- 
pound of  fayalite  (iron-olivine)  green  augite,  and  pyrope,  in 
lenticules  in  granulite  near  Tunaberg,  Sweden  ;  with  thin- 
jointed  structure.     It  is  of  limited  extent. 

(d)  Wehrlite  (v.  Kobell).    A  dark-colored,  coarse-grained 
mixture  of  fresh  olivine  and  green  diallage,  with  abundant 
basaltic  hornblende  and  titaniferous  magnetite.   From  Hun- 
gary, Bosnia,  Finland,  Scotland,  Borneo,  Japan. 

(e)  Saxonite  (Wadsworth).   A  compound  of  serpentinized 
olivine  and  rhombic  pyroxene  (enstatite  or  bronzite) ;  also 
called  "  schiller  rock,"  from  the  alteration  of  the  pyroxene 
to  bastite.    Silica  41.48.    It  is  rarely  found  with  fresh  olivine. 
It  occurs  from  the  Baste,  near  Harzburg,  and  obtained  the 


PRIMARY  ROCKS.  2$  I 

name  "  harzburgite  "  from  Rosenbusch,  which  is  later  than 
that  given  above.  It  is  found  in  the  Alps,  Sweden,  Borneo, 
New  Zealand,  and  in  the  United  States  in  Maryland  with 
bronzite.  Silica  43,  and  Gr.  3.022.  Buchnerite  (Wadsworth) 
is  a  similar  compound  with  additional  augite. 

(/)  Lherzolite  (de  Lametherie).  From  L'herz  in  the 
Pyrenees.  A  coarse-  to  fine-grained  and  compact  compound 
•of  olivine,  diopside  (grass-green  and  like  diallage),  enstatite, 
and  accessory  picotite.  Silica  40-44  ;  Gr.  3.3-3.4.  In  some 
cases  it  is  so  compact  as  to  appear  as  a  monotonously  colored 
serpentine.  Diopside  in  grains  ;  enstatite  yellowish  brown 
to  greenish  gray  with  fibrous  cleavage ;  picotite  is  small 
and  black.  It  occurs  in  great  sheets  in  the  Pyrenees,  Italy, 
Norway,  Tyrol,  Spain,  Maryland,  and  at  Mont  Diablo,  Cal. 
In  Italy  and  Norway  it  is  fresh  ;  in  Germany,  France,  and 
-Cornwall  more  or  less  completely  altered  to  serpentine,  the 
olivine  going  first,  enstatite  next,  diopside  last. 

(g)  Cortlandtite  (G.  H.  Williams).  This  is  Bonney's 
•"  hornblende-picrite,"  and  is  a  compound  of  olivine,  horn- 
blende, and  augite,  and  is  named  from  Cortlandt,  N.  Y., 
where  it  occurs  in  dikes.  It  also  is  found  in  Australia, 
Sumatra,  Custer  County,  Col.  G.  H.  Williams  sug- 
gested that  the  previous  name  "  hudsonite  "  (Cohen)  be 
given  to  the  augite-picrite  type,  while  "  cortlandtite  "  be 
used  for  the  hornblende  variety,  and  Rosenbusch  and  Zirkel 
have  adopted  the  same. 

(It)  Scyelite  (Judd).  From  Loch  Scye,  Scotland,  is  a 
mixture  of  (m)  olivine-green  hornblende  and  biotite. 

(z)  Biotite-olivine  Rock  (Koch).  A  compound  of  fresh 
•olivine  and  great  folia  of  biotite,  rounded  grains  of  spinel 
-of  dark  bluish  green,  titaniferous-magnetite,  accessory 
apatite  and  plagioclase.  Silica  33-35 ;  Gr.  3.27.  From. 
Crittenden  County,  Ky.,  DeWitt,  Ithaca,  N.  Y. 


MANUAL   OF  LITHOLOGY. 


BASALT-GABBRO  INTRUSIVES. 

///.  PYROXENE  SERIES. 
(Necessary  mineral :  Pyroxene.) 

PYROXENITE  (Hunt),  a  general  name  for  an  eruptive 
granular  rock  consisting  of  one  or  more  members  of  this 
mineral  group,  and  equivalent  to  a  gabbro  without  plagi- 
oclase  or  olivine.  Silica  50-55  ;  Gr.  3-3.4.  The  name  has 
nothing  to  do  with  the  pyroxenite  of  Coquand,  which 
refers  to  a  malacolite  rock  in  granular  limestone,  and  is 
wholly  metamorphic.  Rocks  of  this  group  are  reported  from 
Maryland,  North  Carolina,  and  elsewhere.  That  from 
Maryland  consists  of  diallage  and  bronzite. 

The  late  G.  H.  Williams  suggested  the  following  classifi- 
cation : 

With  augite,  Pyroxenite.  From  Cortlandt,  N.  Y.,  Sierra 
Nevada,  Cal. 

With  diallage,  Diallagite.    (See  p.  235.) 

With  bronzite,  Bronzitite. 

With  enstatite  and  diallage,  Websterite.  From  North 
Carolina,  Italy,  etc. 

IV.  MAGNETITE  SERIES. 
(Necessary  mineral :  Magnetite.) 

While  magnetite  is  generally  placed  as  a  metamorphic 
rock  from  contact  action,  there  are  many  cases  where  it  is 
a  distinct  differentiation  of  a  gabbro  magma  with  or  without 
other  typical  minerals  as  accessory.  Many  authorities  hold 
that,  as  magnetite  loses  its  magnetism  at  high  temperatures, 
it  could  not  thus  be  formed.  It  may  be  answered  that  there 
would  be  the  same  argument  against  its  presence  in  basalt 


PRIMARY  ROCKS. 

and  other  truly  eruptive  rocks.  This  series  does  not  pro- 
pose to  claim  for  all  magnetites  an  eruptive  origin,  but  many 
of  them  have  a  decided  one,  as  the  differentiation  of  a 
gabbro  magma  that  has  its  antithesis  in  anorthosite. 
Magnetite  and  anorthosite  are  therefore  "  complementary  " 
rocks.  The  variations  thus  far  noted  are : 

(a)  Magnetite-olivenite  (Sjogren).    From  Taberg,  Sweden, 
composed  of  magnetite  and  olivine  with  a  small  amount  of 
plagioclase,  with  accessory  mica  and  apatite.     Here  it  is  a 
distinct  differentiation  of  a  hypersthene-gabbro. 

(b)  Plagioclase-pyroxene-rc\a.gnetite.  Similar  differentiations. 
From  the  Odenwald,  Frankenstein,  etc. 

(c)  Plagioclase-olivine-m&gnetite,    Cumberlandite    (Wads- 
worth).      From    Cumberland,  R.   I.;    with   silica  21;    with 
feldspar  as  phenocrysts. 

(d)  Pyroxene-magnetite,  Jacupirangite  (Derby). 

(e)  Nep/ietme-0tivtne-isicupira.ngite.     Both  from  Brazil,  as 
differentiations  of  dikes. 


254  MANUAL   OF  LITHOLOGY. 

APPENDIX  TO   GABBRO. 
SERPENTINE. 

Here  are  assembled  entirely  altered  rocks  which  may 
have  originally  consisted  of  olivine,  diorite,  or  gabbro,  as 
these  rocks  pass  (including  all  their  ingredients)  into  this 
mineral,  as  seen  along  the  juncture  of  the  hornblendic  gneiss 
and  Potsdam  quartzite  at  South  Bethlehem  and  at  Easton 
on  the  northern  border  of  the  South  Mountain  in  Pennsyl- 
vania. It  is  therefore  found  in  beds  where  it  has  formed 
from  metamorphic  rocks,  and  in  dikes  where  it  comes  from 
those  decidedly  eruptive.  Under  the  olivine  series  are  given 
a  number  of  instances  of  the  latter  change. 

SERPENTINE. 

A  compact  rock,  dull  in  fresh  fracture,  soft,  with  greasy 
feel ;  usually  dark  green  or  brown. 
Gr.  2.5-2.7. 

It  occurs  compact,  porphyritic  (with  crystals  of  pyrope),. 
slaty,  and  veined.  As  accessories  occur  pyrope,  talc,  bronzite, 
chlorite,  mica,  magnetite,  etc.  Serpentine  is  classed  among 
the  peridotites  from  their  habit  of  weathering,  though  it  is 
derived  from  augitic  and  hornblendic  rocks  through  a 
similar  process.  The  serpentine-quartz  rock  at  South 
Bethlehem,  Pa.,  between  the  gneiss  of  the  South  Mountain 
and  the  overlying  Potsdam  quartzite,  has  been  derived  from 
the  lower  rock  through  change  in  the  hornblende. 


SECONDARY   ROCKS. 

In  contrast  with  primary  rocks,  which  have  been  formed 
by  one  continuous  process  from  a  fluid  magma,  secondary 
rocks  are  those  which  have  been  formed  from  pre-existing 
rocks,  and  which  show  by  texture  or  structure,  or  both,  such 
a  derivation ;  or  they  are  aggregates  of  chemical  or  organic 
forces  through  which  the  weathered  or  soluble  portions  of 
older  rocks  are  gathered  into  masses.  All  of  these  can 
be  distinguished  from  the  rocks  already  described  by  the 
microscope,  if  not  by  the  eye,  though  there  are  transitions 
in  certain  cases  that  will  be  impossible  to  classify  without 
the  microscope. 

The  tendency  in  nature  is  to  stable  compounds.  The 
rotting  of  vegetation  and  the  decay  of  nitrogenous  bodies 
are  paralleled  in  the  "  weathering  "  of  rocks.  In  all  these 
there  is  a  change  from  a  less  to  a  more  stable  compound, 
and,  be  the  process  short  or  long,  there  will  ultimately  be 
reached  a  compound  stable  under  a  continuation  of  the  cir- 
cumstances which  formed  it.  These  circumstances  do  not, 
however,  remain  continuous,  and  the  constant  variations  in 
nature  tend  to  new  combinations.  A  good  example  is  seen 
in  the  action  of  the  oxides  of  iron.  Most  waters  after  soak- 
ing through  the  earth's  crust,  especially  in  volcanic  regions, 
have  minute  percentages  of  sulphuric  acid,  which  dissolves 
whatever  protoxides  of  iron  are  met  with  and  carries  the 
solution  into  the  bodies  of  water  on  the  earth's  surface. 
The  protoxide  at  the  surface  of  the  water  becomes  hy- 

255 


256  MANUAL   OF  LITHOLOGY. 

drated  sesquioxide,  which  is  no  longer  soluble  in  the  acid, 
but  falls  to  the  bottom  of  the  liquid  to  take  oxygen  to  what- 
ever organic  bodies  may  be  there,  and,  being  reduced,  is 
again  soluble  and  brought  to  the  surface,  to  renew  the  oper- 
ation. This  is  but  a  short  cycle  of  changes  ;  others  may 
require  centuries  to  complete.  In  the  previous  pages  min- 
erals have  been  noted  as  undergoing  "  alteration  "  and  form-- 
ing "  secondary  "  minerals,  and  these,  in  their  turn,  have 
been  broken  up  to  make  more  stable  forms — as  the  black 
bisilicates  pass  through  viridite,  epidote,  carbonates,  opa- 
cite,  or  ferrite,  to  form  ferruginous  clays ;  while  feld- 
spars, through  other  lines  of  alteration,  form  lighter  clays. 
Quartzose  rocks,  after  the  weathering  and  levigation  of 
their  unstable  compounds,  are  reduced  to  "  granular"  quartz 
sand.  When  weathering  outstrips  denudation,  the  rocks 
will  have  made  these  changes,  or  have  lost  their  cementing 
media  to  great  depths,  as  in  Brazil,  where  the  elder  Agassiz 
reported  weathering  at  a  depth  of  150  feet.  Incipient 
weathering  proceeds  to  great  depths  even  in  temperate  lati- 
tudes, as  Gallon  states  that  in  Europe  it  is  usually  necessary 
to  strip  away  80  feet  of  slate  outcrop  before  finding  work- 
able stone.  This  is  for  unglaciated  regions  ;  but  in  the  slate 
belt  of  Pennsylvania,  which  was  covered  by  the  furthest 
and  earliest  of  the  ice  advances,  the  average  of  "  mucking  " 
is  but  10  feet,  and  near  Treichler's,  Pa.,  workable  slate  lies 
directly  underneath  glacial  gravel.  Other  good  examples 
of  the  slowness  of  weathering  are  shown  in  the  anthracite- 
coal  basins  around  and  south  of  Hazelton,  which  were  also 
covered  by  the  earliest  ice  advance.  It  is  only  in  these 
regions  that  it  is  profitable  to  "  strip "  the  surface,  and 
throughout  these  regions  anthracite  coal  is  mined  and  sold 
with  no  covering  but  glacial  gravel.  On  the  other  hand, 
the  loss  of  cementing  material  proceeds  to  great  depths. 
In  the  iron  (limestone)  ores  of  the  Clinton  formation,  north 


SECONDARY  ROCKS. 

of  Danville,  Pa.,  the  cementing  calcite  has  been  removed 
over  large  areas  for  500-700  feet  from  the  outcrop  of  the 
beds,  and  deeper  along  the  numerous  faults  that  intersect 
the  region.  The  slight  variation  in  dip  of  surface  and  bed 
makes  this  average  40-60  feet  below  the  surface,  and  the 
removal  has  been  so  complete  that  the  bed  can  be  worked 
with  an  ordinary  pick  or  hoe,  and  the  overlying  shales  have 
lost  their  consistency  and  are  readily  cut  with  a  pick,  unless 
extremely  siliceous.  We  thus  see  that  weathering  pro- 
duces large  masses  of  decomposed  rock  in  place,  and  a 
comparison  of  fresh  and  weathered  rock  shows  us  that  the 
primary  rocks  have  lost  their  alkalies  and  soluble  acids  ; 
while  the  quartz  and  aluminous  silicates  remain.  We  must 
be  prepared,  therefore,  to  find  these  stable  compounds  pre- 
dominant in  secondary  rocks,  unless  changes  have  formed 
new  compounds.  Denudation  tends  to  remove  these  ac- 
cumulated masses  and  distribute  them  under  water  in  lakes 
or  along  seaboards.  The  study  of  orogenic  movements 
shows  us  that  these  sediments  may  be  transformed  into  a 
new  series  of  "  metamorphic  "  rocks,  and  that,  by  similar 
movements,  the  primary  rocks  may  be  similarly  changed 
without  undergoing  weathering  and  denudation.  A  third 
class  of  rocks  is  formed  by  chemical  precipitates  from  sat- 
urated solutions  ;  but  this  is  inconsiderable  in  varieties  of 
rocks  or  bulk.  A  fourth  class  is  due  to  the  secretive  power 
of  organisms  ;  a  fifth  to  the  forces  acting  on  the  country- 
rocks  during  eruption  or  orogenic  movements,  by  which 
comminution  is  produced,  etc.  All  of  these  can  be  grouped 
under  two  heads,  whether  the  masses  retain  their  original 
state  of  aggregation  (subject  to  minor  changes  that  do  not 
constitute  metamorphism),  or  whether  they  have  been  meta- 
morphosed, as: 

I.  Automorphic  Aggregates. 
II.  Metamorphic  Aggregates. 


258  MANUAL  OF  LITHOLOGY. 


I.  AUTOMORPHIC   AGGREGATES. 

In  this  group  the  changes  subsequent  to  aggregation 
must  be  simple  and  due  to  pressure  without  great  heat 
or  other  non-metamorphic  agencies  of  consolidation.  The 
causes  of  aggregation  are  mechanical,  chemical,  and  organic. 
In  each  of  the  classes  the  predominant  force  will  be  one  of 
these  three ;  but  this  does  not  presuppose  that  either  or 
both  of  the  others  cannot  enter  in  a  subordinate  manner. 

Mechanical  Aggregates,  Fragmental  Rocks.  These  are 
formed  and  gathered  by  the  mechanical  forces  of  nature 
from  the  broken  (clastic)  fragments  of  older  rocks,  without 
predominant  chemical  or  organic  action.  The  forces  pro- 
ducing the  comminution  and,  to  a  great  extent,  the  aggre- 
gation are : 

(A)  Hydrogenic,  or  due  to  water  in  forcing  apart  (through 
frost)  the  rocks  and  comminuting  the  fragments :  grinding 
these  during  transportation  and  sorting  them. 

(B)  Pyrogenic,  or  due  to  the  eruptive  forces  which  act 
upon  the  walls  of  fissures,  or  which  produce  finely  commi- 
nuted fragments  of  primary  rocks. 

(C)  Orogenic,   or   due   to   the   crushing    effect   of   earth 
movements. 

(A)  Hydrogenic  Aggregates. 

These  can  be  divided  according  to  the  manner  in  which 
they  were  assembled  by  water,  whether  by  the  liquid  or 
solid  state,  as : 

i.  Aqueous,  where  the  assemblage  was  caused  by  rain, 
streams,  etc.;  and 

(a)  Unsorted   Debris,  where   the   aggregation  is   due   to 
rain,  melting  snow,  or  the  undermining  of  areas  through 
solution ; 

(b)  Stratified  Deposits,  where  the  sorting  and  transport- 
ing power  of  water  have  assembled  the  mass. 


SECONDARY  ROCKS.  2$9 

2.  Glacial,  where  the  assemblage  was  caused  by  ice  in 
the  form  of  glaciers,  and  by  its  ablation. 

(NOTE.  With  the  aqueous  rocks  will  be  noted  the  simi- 
lar forms  produced  by  ^Eolian  forces,  as  they  resemble 
them  lithologically.) 

(B)  Pyrogenic  Aggregates. 

1.  Pyroclasts,  when  the  fragments  have  been  torn  from 
the  sides  of  the  fissures  through  which  the  eruption  was 
made,  or  formed  from  the  eruptive  itself. 

2.  Tuffs,  when   consisting    of   eruptive   ash,  which    has 
been  subsequently  compacted  to  a  greater  or  less  degree, 
and  more  or  less  altered. 

(C)  Orogenic  Aggregates. 

Oroclastic  Breccias,  when  formed  by  orogenic  move- 
ments. 

UNSORTED  DEBRIS. 

The  want  of  stratification  that  characterizes  these  depos- 
its is  also  possessed  by  glacial  aggregates,  especially  the 
stranded  lateral  moraines  on  the  sides  of  valleys,  which  are 
accumulations  of  the  same  ultimate  origin  that  have  been 
moved  further  down  the  valley.  The  ordinary  moraine-stuff 
can  be  distinguished  from  these  deposits  by  the  presence  of 
rocks  foreign  to  the  neighborhood  in  the  absence  of  distinct 
marks  of  glaciation  in  the  mass.  Another  unfailing  dis- 
tinction is  in  the  relative  freshness  of  the  mass  from  top  to 
bottom  of  aj  vertical  section.  Unsorted  debris  is  most 
weathered  at  the  surface,  where  atmospheric  agents  have 
unrestrained  action,  and  possesses  greater  freshness  towards 
the  bottom  of  the  section,  where  the  solid  rock  is  met  with. 
Glacial  accumulations,  on  the  contrary,  have  been  turned 
over  and  thoroughly  mixed,  and  the  time  of  accumulation 
has  been  small  with  respect  to  the  rate  of  weathering  of 


26O  MANUAL    OF  LITHOLOGY. 

rocks;  so  that  the  close  of  the  accumulation  finds  the  mass 
quite  uniformly  weathered  on  a  vertical  section.  If,  how- 
ever, there  should  have  been  a  long  interval  between  the 
beginning  and  end  of  the  aggregation,  we  shall  find  the 
above  order  reversed,  and  the  freshest  material  on  top. 
This  last  state  of  affairs  can  be  met  with  in  ordinary  aggre- 
gation on  a  steep  hillside,  where  the  "  creep  "  produced  by 
rains  or  melting  snows  brings  down  the  slope  fragments  re- 
cently riven  by  frosts  to  cover  older  deposits,  and  there  will 
be  a  transition  from  a  solid  and  fragmental  top  to  a  softer 
and  more  uniform  bottom  ;  but  the  rough,  subangular  out- 
lines of  the  fragments  in  a  "  creep  "  aggregation  cannot  be 
mistaken  for  the  glaciated  rocks  of  a  terminal  moraine.  An 
old  terminal  moraine  would  weather  like  any  other  accumu- 
lation of  material ;  but  on  reaching  its  bottom  we  should 
not  find  the  gradual  transition  to  solid  rock  of  similar  char- 
acter, and  all  the  material  of  the  lower  layer  would  not  be 
equally  fresh.  The  study  of  these  varying  deposits  will  soon 
allow  the  observer  to  distinguish  between  them.  According 
to  the  amount  of  movement  in  gathering  the  mass,  we  can 
distinguish: 

I.  Debris  in  Place.  In  this  case  there  has  been  no 
movement ;  the  rock  has  weathered  above  its  own  outcrop, 
and  at  a  rate  greater  than  that  of  denudation,  so  that  accumu- 
lation has  taken  place.  The  results  of  such  are : 

(a)  Sands,  as  in  the  case  of  quartzose  rocks.  These  sand 
accumulations  are  of  varying  values,  dependent  on  the 
ipurity  of  the  mineral  that  composes  them.  Decomposed 
quartziferous  schists,  gneisses,  etc.,  are  frequently  screened 
to  furnish  sand  for  building  purposes.  The  Oriskany  sand- 
stone of  eastern  Pennyslvania  furnishes  abundant  sands  of  a 
high  character;  the  calciferous  sand-rock  of  Chester  County 
in  the  same  State  furnishes  a  milk-white  sand ;  the  Potsdam 
of  New  York,  and  the  St.  Peter's  of  the  northern  Mississippi 


SECONDARY  ROCKS.  26 1 

basin,  also  furnish  on  weathering  sands  excellent  for  glass- 
making. 

Arkose  (Brongniart)  is  a  sandstone  formed  in  place 
from  the  debris  of  granite,  and  is  styled  "  granitic  sand- 
stone," as  it  contains  quartz,  feldspar,  and  mica  in  clastic 
grains,  and  solidified  by  pressure.  It  was  originally  noted 
in  France,  and  is  found  on  the  borders  of  granitic  masses. 
The  Potsdam  sandstone  at  South  Bethlehem,  Pa.,  rests 
against  the  hornblendic  gneiss  and  granulite  of  the  South 
Mountain,  and  its  lowest  layer  shows  (for  a  few  inches) 
an  abundance  of  feldspar. 

(b)  Clays,  when  argillaceous  or  feldspathic  rocks  weather. 
Granites  form  a  sandy  kaolin  that  can  be  levigated  for  pot- 
tery-making; argillaceous  limestone  loses  its  calcite  and 
forms  brick  and  terra-cotta  clay — if  quartzose  or  flinty,  it 
furnishes  a  poorer  article;  slate  rots  to  bluish  or  reddish 
clays  which  make  good  pressed  brick ;  ferruginous  bands  in 
slates  and  shales  are  fired  for  "metallic"  paint;  the  under- 
shales  of  the  coal  beds  of  the  Appalachian  area  furnish  ex- 
cellent clay  for  fire-brick.  Special  varieties  of  clays  have 
been  thus  named: 

Bituminous  Clay  is  the  decomposed  shales  of  the  Trias 
and  Tertiary  coals  of  Europe.  Of  bluish— or  blackish  gray 
to  black  color;  it  smolders  when  fired,  and  burns  red. 

Saliferous  Clay  is  from  salt  shales  or  marls,  and  contains 
much  chloride  of  sodium,  often  in  crystals,  as  in  the  Salina 
formation  of  the  United  States,  and  elsewhere  in  salt-for- 
mations. 

Alum  Clay  is  a  decomposed  "  alum  shale,"  and  formed 
by  the  weathering  of  the  shale  and  its  pyritiferous  con- 
tent. It  is  common  about  coal  outcrops  that  are  '*  bony" 
and  pyritiferous. 

"Mining"  is  an  earthy  clay  highly  charged  with  carbon 
that  forms  when  a. coal-bed  weathers.  The  name  is  a 


262  MANUAL    OF  LIT  HO  LOG  Y. 

miner's  term.  The  same  term  is  also  used  for  any 
weathered  soft  clayey  rock  that  can  be  readily  worked 
with  a  pick  underground. 

Soft  Ore  is  the  miner's  name  for  the  leached  limestone 
ore  of  the  Clinton  formation  in  the  eastern  United  States. 
Atmospheric  waters  have  removed  the  carbonate  of  lime, 
and  left  the  iron  as  a  mixture  of  carbonate,  clay  and  lim- 
onite  which  is  soft  enough  to  be  dug  out  with  the  fingers. 
It  extends  generally  above  water-level,  and  in  some  cases 
to  one  hundred  feet  below  it,  in  the  vicinity  of  Danville, 
Pa. 

The  secondary  rocks  formed  from  debris  in  place  are 
numerous.  All  the  primary  rocks  of  any  great  development 
have  their  clays  and  earths  formed  from  the  weathering  of 
their  masses,  and  in  this  earthy  or  clayey  matrix  are  held 
angular  and  rounded  pebbles  to  form  their  breccias.  These 
latter  will  be  treated  later  under  the  head  of  "  Megaclastic 
Aggregates,"  as  there  is  very  little  difference,  if  any,  in  the 
appearance  of  a  breccia  formed  in  place,  and  inclosed  in  a 
matrix  of  its  own  rock,  and  the  same  when  moved  a  short 
distance.  The  rocks  forming  in  place  are  all  characterized 
by  a  freedom  from  inclusions.  In  many  cases  the  weathered 
tuff-conglomerates  and  breccias  resemble  the  debris  states 
of  the  same  rock,  as  do  the  weathered  tuffs  the  equally 
weathered  debris ;  but  the  tuffs  usually  contain  bombs,  la- 
pilli,  and  organic  inclusions,  especially  if  they  have  been 
aggregated  by  heavy  rains  or  meltings  of  large  snow  masses, 
while  the  debris  rocks  fall  over  the  outcrop  and  remain  free 
from  intermixtures  with  foreign  substances.  The  following 
conditions  of  weathering  have  been  given  special  names  : 

(c)  Laterite.  This  term  was  originally  given  to  the  weath- 
ering in  tropical  lands  of  a  primary  rock  to  form  a  highly 
ferruginous  clay  that  was  soft  when  dug,  but  hardened  on 
exposure  to  the  air,  and  was  used,  like  adobe,  for  brick- 


SECONDARY  ROCKS.  263 

making.  The  tropical  climate  induces  a  higher  degree  of 
oxidation  than  does  the  more  northern  and  cooler  one,  so 
that  all  rocks  in  hot  countries  tend  to  form  debris  character- 
ized by  ferric  rather  than  ferrous  oxides.  This  has  recently 
been  noted  in  a  comparison  of  the  soils  in  the  northern  and 
southern  States  of  the  Union.  The  above  term  has  been 
extended  to  include  all  weatherings  in  place  attended  by  a 
high  oxidation  of  the  iron  content  and  a  further  impregna- 
tion with  the  same,  and  we  now  have  the  terms  sandstone- 
laterite,  granite-laterite,  tuff-laterite,  etc.,  for  the  above 
conditions  in  these  rocks.  In  Hungary  trachyte-laterite  is 
known  by  the  local  name  nyirock. 

(d)  Wacke.  This  was  formerly  used  to  denote  the  weath- 
ered state  of  a  rock  poor  in  silica,  and  was  afterwards  ex-, 
tended  to  cover  all  weathered  states  of  rocks  by  means  of 
the  adjective  "  wackenitic."  In  Europe  this  survives  in 
"graywacke,"  but  the  term  is  obsolete  here,  and  Dana  ex- 
presses the  state  of  opinion  in  saying  in  his  last  edition  of  the 
41  Manual "  "  which  used  to  be  called  gray  wacke" 

2.  Debris  Slightly  Moved.  These  accumulations  are 
found  on  moderate  slopes,  and  are  usually  of  medium-sized 
fragments,  more  or  less  mixed  with  local  foreign  material  of 
different  origin,  as  : 

(a)  Loam.    A  mixture  of  clay  and  sand  with  more  or  less 
organic  matter  (humus)  of  a  loose  and  earthy  nature,  and 
formed  from  the  washings  of  higher  lands  through  the  action 
of  rain  or  melting  snow.     In  some  countries  the  "  black  soil " 
is  twenty  feet  deep,  as  India — less  so  in  eastern  Kansas  and 
Nebraska. 

(b)  Forest  Soil.     Here  the  loam  is  mixed  with  stumps  and 
limbs  of  trees,  and  accumulations  of  whatever  animals  in- 
habited or  died  in  the  region.     The  amount  of  humus  is 
much  greater  than  in  loam,  and  the  material   more  porous 
and  irregular  in  size  and  character. 


264  MANUAL    OF  LITHOLOGY. 

(c)  Dirt-bed.  A  buried  and  "  fossilized  "  forest  soil,  which 
is  distinguished  from  the  sedimentary  beds  with  which  it  is 
intercalated  by  the  absence  of  stratification  and  the  remains 
of  land  animals  only. 

3.  Agglomerated  Debris.  These  accumulations  are 
found  at  the  bottom  of  high  cliffs,  near  the  bottom  of  steep 
slopes,  and  where  the  tops  or  sides  of  openings  have  fallen 
from  weathering,  or  been  crushed  by  the  removal  of  their 
supports,  as : 

(a]  6Yz^"-agglomerate,  where  the  scaling  of  cliffs  has  heaped 
at  their  foot  (either  above  or  below  water)  an  aggregate  of 
material  of  all  sizes,  from  the  largest  masses  to  the  finest 
clay.  The  interstices  are  filled  by  subsequent  rains  and 
melting  snows,  so  that  the  lower  part  is  a  "  giant  breccia." 
This  is  especially  the  case  where  the  fall  has  taken  place  into 
water  of  considerable  depth,  and  thus  unaffected  by  wave 
action. 

(If)  5/^-agglomerate,  where  the  material  has  slid  down 
a  steep  slope  gradually.  Here  the  descent  has  been  gradual, 
and  the  material  is  generally  of  smaller  sizes  and  more  uni- 
formly compact. 

(c)  £dw-agglomerate,  where  rubbish  has  accumulated 
in  a  cavern  by  the  gradual  falling  of  the  roof,  and  has  been 
mixed  with  washings  into  the  cavern,  as  well  as  cemented 
by  whatever  was  held  in  solution  by  percolating  waters. 
Under  this  German  authorities  name  especially 

Haselgebirge.  In  the  salt  region  of  the  northern  Alps, 
where  agglomerates  have  been  formed  with  a  clay  matrix 
by  the  caving  in  of  caverns  washed  out  of  the  rock  salt. 

(d]  Eruptive-agglomerate,  where  large  blocks  have  fallen 
into  an  old  crater  or  on  its  slopes,  and  have  been  cemented 
by  a  new  flow  from  the  same  crater  or  an  adjacent  one.  In 
this  case  the  cemented  fragments  are  universally  formed  by 
the  weathering  of  an  old  lava,  and  are  not  pyroclasts. 


SECONDARY  ROCKS.  265 

STRATIFIED  AQUEOUS  DEPOSITS. 
These  are  accumulations  which  have  been  transported  and 
sorted  by  water,  and  which  are  more  or  less  homogeneous 
in  composition.     According  to  the  size  of  the  particles,  they 
can  be  divided  into : 

1.  Aggregates  whose  particles  can  be  suspended  in  or 
pushed  by  water  moving  with  slight  rapidity,  as  a  river 
after  it  leaves  the  piedmont  portion  of  its  course ;  or  micro- 
clastic. 

2.  Aggregates  whose  particles  are  too  large  to  be  so 
suspended  or  moved  ;  as  megaclastic. 

I.  Microclastic  Aggregates.  These  are  loose  or  solid, 
and  may  be  divided,  according  to  the  chemical  composition 
of  the  materials  into : 

(a)  Argillaceous. 

(b)  Mixed. 

(c)  Quartzose. 

ia.   LOOSE  ARGILLACEOUS  AGGREGATES. 

CLAY. 

A  compound  of  kaolin  (hydrated  silicate  of  alumina)  with 
silica,  iron,  lime,  magnesia,  potash,  soda,  and  varying 
amounts  of  impurities,  among  which  may  be  noted 
mica  and  partly  decomposed  feldspar.  It  is  white 
when  pure,  but  is  colored  in  shades  of  yellow  and 
red  through  brown  to  black.  Pure  kaolin  and  dry 
clay  are  not  plastic,  but  generally  fall  to  an  impal- 
pable powder ;  when  moistened  with  water,  it  is  more 
or  less  plastic  ;  when  fired,  it  becomes  hard  and  stony : 
when  dry  and  breathed  upon,  it  gives  a  characteristic 
odor  (whence  the  term  "clayey  "  odor),  and  it  adheres 
to  the  tongue. 

Silica  40-90;  Gr.  1.75-2 ;  when  heated  at  100°  C.f 
2.44-2.47. 


266  MANUAL    OF  LITHOLOG  Y. 

These  compounds  are  valuable  on  account  of  their  plas- 
ticity, and  this,  as  shown  by  Cook,  depends  on  their  fineness. 
After  strong  heating  the  combined  water  is  driven  off  and 
the  plasticity  is  lost,  unless  finely  ground  and  allowed  to 
stand  with  water.  The  color  of  clay  is  due  to  the  impuri- 
ties— chiefly  iron  in  the  form  of  protoxide,  which  is  con- 
verted to  the  higher  oxide  by  firing.  Calcite  neutralizes  the 
coloring  effect  of  iron,  so  that  a  marly  clay  will  burn  to  a 
"  cream  "  color  instead  of  red.  Sedimentary  clays  are  found 
scattered  throughout  the  world  wherever  deep  water  and 
gentle  currents  prevail.  They  can  be  told  from  glacial 
clays  by  their  stratification,  and  the  arrangement  of  their 
foreign  burden  in  parallel  lines  and  with  the  longer  axes  (if 
unequiaxial)  parallel  to  the  stratification.  Glacial  clays  are 
generally  more  siliceous,  and  usually  abound  in  foreign  ma- 
terial of  all  sizes,  and  this  is  arranged  haphazard,  with  no 
attempt  at  what  has  just  been  described.  Clays  joint  on  dry- 
ing and  become  friable.  A  "  fat "  clay  is  tough  and  plastic, 
and  with  not  much  foreign  matter ;  a  "  lean  "  clay  is  sandy, 
and  therefore  "  loose  "  and  with  little  plasticity.  We  can 
distinguish : 

1.  Kaolin  (see  under  "  Minerals  as  Rocks"). 

2.  Pipe-clay,  Plastic  Clay.     A  white  clay  (therefore  free 
from  iron)  of  nearly  pure  kaolin. 

3.  Brick-clay,  Tile-clay.     An  impure  clay  with  a  high  per- 
centage of  iron  (6-8  per  cent)  used  for  brick,  tiling,  terra- 
cotta.   Clay  with  90  per  cent  of  silica  has  been  used  for  mak- 
ing brick. 

4.  Paint-clay.     The  washings  from  limonite  ores  are  now 
used  for  burning  to  make  "  metallic"  paint.    This  is  a  highly 
ferruginous   clay  and  is  accumulated  in  settling  ponds  to 
which  the  wash-waters  from  limonite  workings  run.    It  also 
deposits  from  mine  water. 

5.  Fire-clay,  with  little  iron  and  but  traces  of  the  alkalies 


SECONDARY  ROCKS.  267 

and    lime.     When  the  impurities  run  above  4  per  cent,  it 
loses  its  refractory  nature.     Silica  average  72. 

6.  Fuller  s-earth.  A  somewhat  greasy,  earthy,  and  soft  sub- 
stance with  greasy  streak,  with  light  shades  of  green  and 
brown,  that  falls  to  mud  on  placing  in  water  and  is  not  plas 
tic.  It  is  found  on  the  Rhine,  in  Belgium,  Saxony,  and 
England,  usually  as  a  formation  in  the  Jurassic  and  Creta- 
ceous ;  but  in  some  cases  it  is  the  result  of  the  weathering  of 
gabbro-,  hornblende-,  and  greenstone-schists. 

\b.  LOOSE  MIXED  AGGREGATES. 
MUD. 

An  indefinite  term  applied  to  microclasts  of  varying 
composition  when  mixed  with  much  water.  In  gen- 
eral it  may  be  defined  as  an  impure  clay  with  abun- 
dant proportions  of  fine  sand,  and  whatever  material 
happens  to  be  abundant  at  the  place  where  it  forms. 
It  occurs  at  the  surface  of  the  earth  after  rain,  be- 
hind dams,  in  the  mouths  of  rivers  that  empty  into 
sounds,  and  where  the  tide  has  little  scouring  effect, 
etc.  When  compact,  it  forms  "  mudstone." 

In  general,  this  compound  has  little  claim  for  a  place  in 
lithology,  but  it  has  been  found  in  the  "  Bad  Lands "  of 
South  Dakota,  filling  dikes  by  injection  from  below,  as  in 
the  case  of  igneous  rock.  This  is  shown  by  the  unstratified 
state  of  the  filling  and  the  want  of  arrangement  of  unequi- 
axial  particles  relative  to  the  dike-walls.  A  mixture  of  pure 
clay  with  much  water  is  also  called  "  mud,"  as  is,  in  fact, 
any  similar  mixture  of  fine  earthy  materials.  Under  this 
can  be  placed : 

1.  Alluvium.     The  earthy,  clayey  deposit  from  flooded 
rivers  upon  low  lands,  which  varies  in  size  of  grains  with 
the  velocity  of  the  waters. 

2.  Silt  is  the  same  in  origin,  but  mixed  with  the  finer 


268  MANUAL   OF  LITHOLOGY. 

material  carried  by  low  water  and  deposited  on  a  small  scale 
behind  dams,  and  on  a  larger  one  in  the  mouths  of  rivers 
and  over  broad  bays  into  which  they  empty.  We  speak  of 
the  "  silting  "  of  a  river  or  bay,  and  refer  to  the  filling  of  the 
muddy  bottom,  and  the  encroachment  of  the  muddy  shores. 
This  is  shown  on  a  grand  scale  along  the  Atlantic  coast  of 
the  United  States,  where  the  rivers  empty  behind  sandy 
barriers  and  where  there  are  broad  sounds  between  the 
ocean  and  the  land — from  New  Jersey  to  Georgia. 

3.  Loess.      An    earthy,    clayey   deposit   (frequently   cal- 
careous, with  marly  nodules)  forming  unstratified  layers  in 
valleys,  but,  unlike  alluvium,  of  wind-drift  origin.     This  is 
included  with  aqueous  deposits  from  its  association  with 
and  its  likeness  to  them. 

4.  Adobe.     A  similar  deposit  in  the  arid  regions  of  the 
western  States  of  the  Union,  consisting  of  calcareous  clay 
mixed  with  angular  quartz  grains  of  great  fineness,  and  folia 
of  mica  arranged  haphazard.     Of  wind  origin  ;  unstratified, 
and  used  for  the  making  of  brick  ;  hence  the  names  "  adobe  " 
brick,  "  adobe  "  house.     The  winds  from  the  Mojave  Desert 
in  California  bring  to  the  coast  an  abundance  of  this  fine 
dust,  so  that  the  sun  is  almost  obscured.    Similar  accumula- 
tions of  wind  and  muddy  wagon-wheels  are  seen  in  the 
buried  cities  of  the  East,  old  Rome  being  twenty  feet  below 
the   present  city   level  from   this   cause.     The   American 
"  adobe  "  deposit  is  from  2000  to  3000  feet  thick. 

ic.  LOOSE  QUARTZOSE  AGGREGATES. 
SAND. 

An  aggregate  of  loose  mineral  grains  (usually  of  quartz) 
varying  in  size  from  impalpable  dust  to  an  eighth  of 
an  inch.  With  the  quartz  are  associated  feldspar, 
mica,  dolomite,  calcite,  magnetite,  and  (less  frequently) 
other  minerals. 


SECONDARY  ROCKS.  269 

This  is  the  accumulation  of  the  last  states  of  the  stable 
mineral  components  of  rocks,  and,  though  the  accumulations 
are  mainly  due  to  water,  a  large  number  are  due  to  wind,  as 
in  deserts  and  along  sandy  shores.  The  shape  of  the  grains 
varies,  but  it  can  generally  be  said  that  the  most  angular 
grains  are  found  nearest  the  origin  of  the  sand,  and  that  at- 
trition and  transportation  round  the  edges  rapidly,  so  that 
in  studying  the  grains  of  sand  of  a  peculiar  nature  from  its 
origin  to  varying  distances  along  a  given  line  it  was  found 
that  the  greater  the  distance  from  the  origin  the  more 
round  the  form.  In  general,  it  can  be  said  that  sands  due  to 
weathering  and  denudation  of  rocks  by  ordinary  processes 
are  by  no  means  so  sharp  and  angular  as  those  due  to  glacial 
action ;  and  in  the  case  of  fine  sands  and  clays  of  glacial 
origin  there  is  a  decided  glimmer  to  the  cloud  obtained  bv 
stirring  in  water  that  is  absent  in  those  of  ordinary  origin, 
unless  they  happen  to  be  quite  micaceous,  and  then  the 
glimmer  is  pearly  rather  than  vitreous.  The  following  are 
.some  of  the  more  important  mineral  varieties  of  sand  : 

i.  Magnetite-sand.  Found  in  rivers  and  along  the  coasts 
of  regions  where  primary  rocks  exist.  In  many  cases  the 
sands  are  worked  by  magnetic  separation  for  the  mag- 
netite. 

2.  Gold-bearing  Sand.   Found  where  rocks  containing  gold 
have  weathered.     California,  Australia,  the  Urals,  etc.,  are 
historical   for  the   amounts   of    the   precious   metals  thus 
found. 

3.  Diamond-sand.    From  Brazil,  and  formed  of  the  debris 
of  itacolumite.     This  contains  also  topaz,  hyacinth,  garnet, 
-emerald. 

4.  Tin-sand  is  the  debris  of  greisen,  and  is  found  most 
extensively  formed  at  Banca  and  Billeton,  in  the  Straits  of 
Malacca,  and  less  extensively  in  Cornwall  and  other  tin* 
bearing  regions,  as  the  Dakota  Black  Hills. 


2/0  MANUAL   OF  LITHOLOG  Y. 

5.  Crystal-sand,  where  the   original  clastic  grains  have 
been  built  upon  by  quartz  from  solutions  until  a  crystal  out- 
line has  been  formed  by  what  Dana  styles  crystallinic  meta- 
morphism.     This  is  occasionally  found  in  loose  sand,  but  the 
process  usually  compacts  the  mass  into  sandstone. 

6.  Calcareous  Sand  is  formed  on  coral  reefs  and  other  cal- 
careous formations,  and  is  usually  soaked  in  so  strong  a 
cementing  material  that,  though  it  can  be  readily  dug  with 
a  spade  and  cut  into  various  shapes,  it  soon  hardens  to  a 
solid  and  somewhat  friable  rock. 

7.  Anthracite-sand.     For  a  short  time  after  the  wreck  of 
one  of  the  Philadelphia  &  Reading  colliers  north  of  Minot's 
Ledge,  on  the  Massachusetts  coast,  the  beach  was  lined  with 
anthracite  sand  and  gravel,  but  the  wave  action  soon  re- 
duced it  to  impalpable  powder  and  it  disappeared.     It  fur- 
nished  a  good  example  of  the  "  rolling  "  power  of  water. 

8.  Pumice-sand  is  found  on  the  shores  of  the  volcanic 
regions  of  south  Italy,  the   Island  of  Teneriffe,  the  lake  of 
Laach,  and  in  other  volcanic  regions  bordering  on  the  water, 
where  the  waves  can  work  over  the  debris  and  tuffs  to  form 
sand. 

(Blown  Sand  bears  to  ordinary  sand  the  same  relation 
that  loess  does  to  clay,  as  it  is  a  wind  accumulation,  and 
found  in  deserts  and  along  shores.  These  are  sometimes 
called  jEolian  formations.) 

SOLID   MICROCLASTIC   AGGREGATES. 

These  can  be  grouped  under  two  general  heads  :  those 
with  predominant  clay,  and  those  with  predominant  quartz. 
The  claystones  and  mudstones  gradually  shade  into  one 
another,  and  are  distinct  from  the  sandstones.  These  rocks 
have  been  cemented  together  by  various  media :  pressure 
(with  or  without  heat  and  moisture),  solutions  of  various 
compounds — siliceous,  calcareous,  ferruginous,  etc.  They 


SECONDARY  ROCKS. 

may  be  of  any  color  from  white  to  black  through  yellows, 
reds,  blues,  and  browns,  less  frequently  greens,  depending 
on  the  presence  of  iron,  manganese,  carbon,  etc. 

I.  CLAYSTONE. 

A  compact  and  tolerably  solid  mass  consisting  of  clay, 
not  cleavable,  and  fracturing  readily  in  any  direction  ; 
variously  colored. 

This  is  the  hardened  sediment  called  "  clay,"  and  not  the 
weathered  aggregate  of  pyroclasts  called  "  tuff."  It  is  dis- 
tinguished from  the  slates  and  shales  by  its  want  of  regular 
fracture,  as  well  as  its  inferior  hardness  and  lower  content 
of  foreign  admixtures. 

II.  SHALE,  Argillaceous  Shale. 

A  claystone  which  clea«ves  readily  along  its  planes  of 
stratification,  but  which  shows  no  slaty  cleavage.  It 
is  a  consolidated  clay  or  mud,  and  usually  gray  to 
black  in  color,  with  infrequent  greenish,  reddish,  or 
purplish  shades. 

This  is  a  softer  rock  than  clay  slate,  owing  to  the  absence 
of  the  pressure  which  in  the  latter  produced  cleavage.  It- 
frequently  contains  folia  of  mica,  abundance  of  quartz  sand, 
and  other  impurities  that  form  the  varieties  named  below. 
It  shades  into  clay-slate  in  some  localities,  and  into  flagstone 
(by  predominance  of  quartz).  The  varieties  are  : 

1.  Schieferletten,   Rcthelschiefer   (Gumbel).      This   is   a 
variegated  shale  with  a  greasy  feel ;    easily  fractured,  and 
carrying  a  good  deal  of  water,  so  that  it  is  still  somewhat 
plastic.     It  is  an  imperfectly  solidified  claystone. 

2.  Bituminous  Shale,   with  a  small  amount  of  bitumen  ; 
of  a  dark-brown  color.     This  will  not  burn  by  itself,  and  is 
thus  distinguished  from  the  "  Brandschiefer,"  which  will. 


2/2  MANUAL   OF  LITHOLOGY. 

3.  Carbonic  Shale,  with  more  or  less  carbon  intimately 
mixed    with   it ;    of  medium   fine-grain ;   bedding-cleavage  ; 
shelly,  splintery  fracture  across  the  cleavage  ;    black  color, 
and  considerable  percentage  of  iron,  through  the  increase  in 
which  .it  shades  into  "  black-band  "  ironstone.     It  occurs  as 
41  partings  "  in  coal-beds,  and  burns  fiercely  in  culm-banks, 
as  its  porosity  furnishes  sufficient  air  for  combustion.    When 
the  "  cut-off  "  was  dug  to  isolate  the  fire  in  the  Butler  mine, 
near  Pittston,  Pa.,  the  traces  of  a  previous  fire  were  found 
that  had  left  the  masses  of  the  coal  pillars  intact,  but  had 
burned  to  ash  the  partings  formed  of  coal  shale  throughout 
a  large  area,  and  on  an  average  of  eight  to  ten  feet  from  the 
air. 

4.  Micaceous  Shale.     A  sandy  shale  with  abundant  flakes 
of  mica  found  in  the  coal  measures. 

5.  ^/ww-shale.     A  pyritiferous  shale  associated  with  the 
coal,  and  wherever  organic  accumulations  were  sufficiently 
abundant  to  reduce  the  iron  slimes  in  waters  carrying  sul- 
phuric acid,  by  combining  their  oxygen  with  the  organic 
carbon  or  hydrogen.     It  is  usually  dark-gray  to  black,  and 
the  pyrite  is  interlaminated  with  the  clay  or  aggregated  in 
masses  from   the  size  of  peas  to  several  feet  in  diameter. 
This  is  readily  weathered  to  form  alum-clay. 

III.  CLAY-SLATE. 

A  compact  fissile  claystone — usually  colored  dull  blue 
or  bright  red  (also  purple,  green,  brown,  and  black) — 
with  occasional  admixtures  of  quartz  and  other  min- 
erals. The  cleavage  is  quite  perfect  with  respect 
to  a  plane  which  may  or  may  not  correspond  to  that 
of  deposition,  and  may  be  produced  by  pressure,  or 
by  the  arrangement  of  abundant  unequiaxial  minerals 
parallel  to  the  plane  of  deposition. 

Silica  40-75  (average  60)  ;  Gr.  2.5-2.85. 


SECONDARY  ROCKS.  2/3 

According  to  whether  the  cleavage  is  irregularly  ar- 
ranged with  respect  to  the  bedding  plane,  or  generally 
follows  it,  we  can  arrange  the  above  rocks  into  two  general 
groups : 

I.  ARGILLITE,  Clay-slate. 

A  rock  with  composition  as  above  stated,  but  with  few 
impurities,  and  with  well-developed  slaty-cleavage  at 
any  angle  to  the  bedding  plane. 

This  is  the  ordinary  clay-slate,  and  is  generally  found  in 
the  older  formations  where  beds  of  clay  have  been  subjected 
to  high  pressures.  In  some  cases,  and  generally  in  the 
harder  slates,  the  pressure  has  destroyed  the  bedding- 
cleavage,  but  in  the  softer  varieties  it  remains  highly  devel- 
oped. In  this  rock  there  are  few  inclusions,  and  the  hard- 
ness is  due  solely  to  pressure.  The  binding  material  is 
usually  a  small  amount  of  carbonate  of  lime. 

(a)  Roofing  Slate.     This  is  dark-colored  from  carbon,  or 
red  from  ferrite.     It  should  be  free  from  inclusions,  from 
admixtures  of  pyrite  and  other  efflorescent  minerals,  and 
from  sand. 

(b)  Ordinary  Clay-slate.     A  variety  of  the  above  without 
the  high  degree  of  cleavage  necessary  for  roofing  purposes, 
and  with  abundant  inclusions  of  other  minerals. 

(c)  Pinsill,  Pencil  Slate.      This  soft  variety  retains  the 
bedding-cleavage,   and   breaks   readily   into    long    slender 
prisms  used  for  slate-pencils  (whence  the   Welsh  name) ; 
also  found  in  the  Thuringian  Forest. 

(d)  Black  Chalk.     A  soft  and  highly  carbonaceous  clay 
slate  used  for  marking  purposes.     Found  associated  with 
clay-slate  in  the  Thuringian  Forest,  Spain,  etc. 

(e)  Carbonaceous  Clay-slate  is  a  transition  into  the  above 
and  into  alum  shale. 


274  MANUAL    OF  LITHOLOGY. 

(f)  Calcareous  Clay-slate,  where  the  cementing  medium 
is  highly  prominent,  and  forms  nodules  in  the  mass,  as  well 
as  lighter  bands. 

The  argillites  are  found  in  the  regions  of  metamorphic 
rocks,  and  pass  by  regular  gradations  into  the  crystalline 
schists.  In  the  United  States  roofing  slates  are  found  in 
Vermont  and  Pennsylvania.  In  the  latter  State  they  occur 
in  the  Hudson  and  Marcellus  formations ;  mainly  in  the 
former. 

2.  PHYLLITE. 

A  clay-slate  with  abundant  mica,  a  greater  tendency  to 
a  crystalline  texture,  a  greater  luster,  and  a  larger 
proportion  of  microcrysts  uniformly  scattered 
throughout  the  mass ;  with  cleavage  sometimes 
parallel  to  the  bedding-planes,  and  due  solely  to 
sedimentation. 

This  variety  includes  two  dissimilar  types : 

(a)  Micaceous  Clay-slate.   A  slate  cleavable  parallel  to  the 
bedding  planes  due  to  the  pressure  of  the  superincumbent 
mass  and  to  an  abundance  of  folia  of  mica  arranged  parallel 
to  the  bedding,  as  is  shown  by  the  intercalation  of  strata  of 
grits  and  sands  in  the  slate  measures. 

(b)  Phyllite   Proper.      A  highly   crystalline   slate ;   with 
perfect  cleavage  normal  to  the  pressure  (or  inclined  to  it, 
see  Becker's  experiments) ;  with  a  higher  content  of  mica 
than  that  possessed  by  argillite,  and  much  quartz,  chlorite, 
feldspar,  and   rutile,   and   yet   retaining   the   evidences   of 
sedimentation,   and   not    subjected   to    either    regional   or 
contact  metamorphism,  as  far  as  the  formation  of  "  contact " 
minerals.     The  foreign  minerals  may  have  entered  the  mass 
as  sediments  from  older  rocks,  or  as  crystallizations  due  to 
the  pressure  which  produced  cleavage.     Argillite  shades 


SECONDARY  ROCKS. 

into  phyllite,  and  the  latter  may  be  taken  as  the  intermediate 
state  between  argillite  and  argillaceous  mica-schist.  In 
general  phyllite  can  be  told  from  argillite  by  its  higher 
luster.  Many  authorities  class  phyllite  with  the  meta- 
morphic  schists  on  account  of  the  content  of  crystalline 
minerals ;  but  Geikie  states  that  no  line  can  be  drawn  be- 
tween them,  and  Dana  places  them  together. 

SOLID  QUARTZOSE  MICROCLASTIC  AGGREGATES. 
SANDSTONE. 

A  rock  composed  of  consolidated  sand  of  any  kind.  Ac- 
cording to  the  predominant  mineral,  we  may  have 
siliceous,  granitic,  micaceous,  feldspathic,  calcareous, 
etc.,  varieties. 

Sandstones  vary  in  regard  to  their  cementing  medium. 
It  is  generally  siliceous  or  argillaceous ;  but,  as  in  the  Oris- 
kany  sandstone  of  eastern  Pennsylvania,  it  is  calcareous,  and 
a  short  exposure  to  the  weather  causes  the  bands  with  this 
cement  to  crumble  to  sand.  In  many  cases  beach  sands  with 
a  large  content  of  shell  fragments  are  more  or  less  con- 
solidated from  the  solution  of  the  shells  by  meteoric  water. 
Infiltrations  of  ferruginous  solutions  usually  cement  the 
lower  layers  of  sand  that  rest  against  a  non-porous  medium 
with  hydrated  sesquioxide  of  iron,  to  form  a  ferruginous 
sandstone,  in  case  the  amount  of  iron  is  small ;  if  large,  a 
siliceous  limonite  is  the  result.  As  sandstones  are  sediment- 
ary deposits,  they  are  stratified ;  but  the  conditions  of 
deposit  may  have  been  such  as  to  permit  one  series  of  forces 
to  act  during  a  long  period,  so  that  the  deposit  for  the 
period  was  uniform,  and  the  layer  of  rock  of  great  thickness. 
A  succession  of  long  and  uniform  intervals  will  produce  a 
thick-bedded  rock;  of  short  periods,  a  thin-bedded  rock;  and 
of  very  short  periods,  a  laminated  rock.  Sandstones,  accord- 


276  MANUAL   OF  LITHOLOGY. 

ing  to  the  nature  and  strength  of  the  cementing  medium,  are 
compact,  friable,  and  incoherent.    Some  of  the  varieties  are  : 

1.  Ferruginous  Sandstone,  where  the  cementing  medium 
is  iron  with  a  varying  amount  of  clay.     According  to  the 
form  of  this  element  we  have : 

(a)  Red  Sandstone,  where  the  anhydrous  oxide  is  pres- 
ent.    Dana  says  that  this  form  of  oxide  is  due  to  the 
heated  condition  of  the  waters  in  which  the   sediments 
were  deposited. 

(b)  Yellow  Sandstone,  where  the  hydrous  oxide  is  pres- 
ent.    Both  of  these  are  taken  as  evidence  of  scarcity  of  life 
in  the  area  of  deposition,  or  the  organic  aggregates  would 
have  been  oxidized  at  the  expense  of  the  sesquioxides,  and 
they  would  have  been  reduced  to  protoxides,  and,  as  such, 
would  not  have  colored  the  stone. 

2.  Argillaceous  Sandstone  is  where  the  cement  is  clay,  and 
this  can  be  recognized  by  its  odor,  as  stated  under  "  Clay. " 

3.  Calcareous  Sandstone,  where  the  cement  is  carbonate 
of  lime,  as  in  some  bands  of  the  Oriskany  sandstone,  noted 
above. 

4.  Siliceous  Sandstone,  where  the  cement  is  silica. 

5.  Grit     A  sandstone  where  the  grains  are  sharp  and  of 
the  largest  size  (one-eighth  of  an  inch). 

6.  Flagstone.  A  thin-bedded  stone  easily  capable  of  being 
split  parallel  to  the  bedding,  and  furnishing  large  slabs  for 
paving  and  flagging.     This  is  sometimes  called  laminated, 
and  some  authorities  state  that  the  tendency  is  due  to  minute 
particles  of  mica.     The  slabs  have  evidently  possessed  an 
incipient  tendency  to  separate  in  the  mass,  as  their  faces  are 
frequently  covered  with  dendritic  markings,  as  are  the  joint 
faces  of  other  rocks. 

7.  Micaceous    Sandstone.    A  rock  with  much  mica.    The 
micaceous  sandstones   of  the   anthracite-coal  measures  of 
Pennsylvania  carry  a  large  mica  content,  as  well  as  a  large 


SECONDARY  ROCKS.  2/7 

percentage  of  carbon,  and  their  tendency  to  split  in  thin 
laminae  is  due  to  the  mica,  which  shows  readily  in  silvery 
folia  against  the  black  background.  It  is  also  called  fissile 
sandstone.  "Ganister"  belongs  here. 

8.  Freestone.    This  term  is  applied  by  quarrymen  to  any 
stone  that  breaks  equally  well  in  all  directions.     The  "  brown- 
stories  "  used  in  facing  buildings  in  the  eastern  United  States 
are  examples  of  this  variety. 

9.  Kaolin-sandstone,  with  kaolin  as  a  cementing  medium. 
A  rare  stone,  found  in  the  Thuringian  Forest,  and  from  its 
refractory  nature  used  for  lining  furnaces. 

10.  Asphaltic  Sandstone,  where  asphalt  is  a  cementing 
medium.     Of  limited  occurrence  in  Europe. 

11.  Crystal-sandstone,  where  the  grains  have  been  fur- 
nished with  crystal  planes  and  terminations  by  crystallinic 
metamorphism.     These  occur  in  the  older  sandstones. 

12.  Buhrstone.      A  highly  siliceous  and  cellular  rock 
found  in  the  Tertiary  of  Paris,  and  extensively  worked  for 
millstones.     Also  found  in  South  Carolina. 

13.  Dike-sandstone.     This  is  the   unstratified   filling  of 
dikes  in  various  rocks  which  have  been  filled  in  the  usual 
way  by  injections  from  below,  as  the  unequiaxial  minerals 
are  arranged  haphazard  without  any  relation  to  the  dike- 
walls  or  the  horizontal  plane. 

14.  Feldspathic  Sandstone  is  found  near  granitic  out- 
crops.    The  lower  portion  of  the  Potsdam  sandstone   at 
South    Bethlehem   is    somewhat    feldspathic.     A    greater 
amount  of  this  mineral  would  form  arkose. 

SAND-ROCK  (Dana). 

A  rock  made  of  sand  of  any  kind,  especially  if  not  sili- 
ceous or  granitic. 

In  this  rock  the  predominant  mineral  is  not  quartz,  but 


278  MANUAL   OF  LITHOLOGY. 

.a  small  amount  of  quartz  may  enter  without  placing  the 
•compound  among  the  sandstones.     As  varieties  are  : 

1.  Calcareous  Sand-rock  is  made  of  comminuted  corals, 
shells,  etc. 

(a)  Coquina  (Spanish  local  name)  is  the  shell  rock  of 
Florida,  which  is  soft  when  excavated,  but  soon  hardens, 
as  seen  in  the  old  walls  and  buildings  of  St.  Augustine,  Fla. 

2.  Glauconite   Sand-rock,  when   composed   of  grains   of 
green  earth  and  quartz. 

3.  (Arkose  has  already  been  noted  on  p.  261.     It  is  a  com- 
pound of  feldspar,  quartz,  and  varying  amounts  of  mica,  and 
is  found  at  or  near  the  outcrops  of  granite  or  gneiss.) 

4.  Serpentine  Sand-rock  is  found  on  the  Isle  of  Rhodes, 
as  the  result  of  the  alteration  and  weathering  of  a  basic  vol- 
canic rock. 

MEGACLASTIC   STRATIFIED   DEPOSITS. 

These  deposits  are  composed  of  materials  usually  greater 
than  \  inch,  and  are  collected  by  flooded  and  torrential 
streams,  and  energetic  wave  action.  The  deposits  are  dis- 
tinguished by  the  shape  of  their  materials,  and  upon  this 
shape  depends  the  length  of  time  during  which  they  were 
being  assembled  and  the  name  by  which  they  are  known,  as  : 

Breccia. 

Angular  fragments  of  minerals  or  rocks   firmly  ce- 
mented together  by  some  matrix  or  binding  medium. 
Brecciola  (Brongniart). 

A  breccia  composed  of  small  fragments. 
Conglomerate. 

A  rock  composed  of  rolled  pebbles  or  stones  cemented 

in  any  manner. 
Pudding-stone. 

A  conglomerate  with  rounded  stones  (Dana). 


SECONDARY  ROCKS. 

Gravel. 

A  loose  and  uncemented  accumulation  of  rolled  stones 

and  sand  of  moderate  sizes. 
Shingle. 

An  accumulation  similar  to  gravel,  but  of  larger  stones 

and  without  sand. 
Hard-pan. 

An  accumulation  of  any  of  the  above  forms  sufficiently 
cemented  to  break  in  masses,  but  readily  broken  up 
with  the  pick  or  bar. 

The  above  rolled  varieties  are  mainly  of  quarts,  as  no 
other  mineral  can  last  under  the  strong  grinding  induced  by 
such  powerful  and  long-continued  forces.  The  breccias  may 
be  formed  of  any  of  the  foregoing  rocks.  Conglomerates 
are  consolidated  shingles  and  gravels,  and  the  latter  are 
found  where  strong  currents  would  sweep  away  the  sands 
and  roll  the  larger  fragments.  Breccias  are  found  near  the 
outcrops  of  the  rocks  from  which  they  have  been  broken. 
The  greater  the  distance  of  transportation  the  greater  the 
loss  of  angular  contour  and  the  more  the  rounding,  as  well 
as  the  greater  per  cent  of  loss  from  abrasion,  so  that  only  the 
hardest  rocks  reach  the  accumulations  of  gravel  and  shingle, 
or  remain  there  long,  and  the  quartz  rocks  and  siliceous 
porphyries  alone  resist  the  combination  of  grinding  and 
weathering  to  which  such  aggregates  are  subjected.  The 
classification  of  conglomerates  and  breccias  has  been 
abandoned  by  most  authorities  on  the  ground  that  both  the 
material  of  the  angular  or  rolled  fragments  and  of  the  ce- 
menting matrix  should  be  considered.  The  latter  may  be 
argillaceous,  calcareous,  ferruginous,  or  siliceous,  and  the 
fragments  of  any  rock  may  be  bound  by  any  one  of  the 
above,  or  by  a  weathered  portion  of  the  same  rock.  These 
rocks  will  be  distinguished  from  pyroclastic  and  oroclastic 
breccias  and  conglomerates  by  their  cementing  media.  It 


28O  MANUAL    OF  LITHOLOG  Y. 

is  proposed  to  classify  all  conglomerates  and  breccias,  ac- 
cording to  the  cementing  media  and  the  material  of  which 
they  are  composed,  as  follows : 

I.  The  cementing  medium  is  of  the  same  nature  as  the 
included  fragments  (either  fresh  or  weathered)  and  formed 
by  ordinary  agencies.     For  such   rocks  the  terms  "  quartz" 
conglomerate,  "  quartz  "  breccia,  "  trachyte  "  breccia,  "  por- 
phyry "  conglomerate,  "  slate  "  breccia,  "  limestone  "   con- 
glomerate, will   be   used.      These    are   <£#m-breccias   and 
conglomerates. 

II.  The  cementing  medium  is  different  from  the  inclosed 
fragments,  and  may  be : 

(a)  Siliceous.     A  breccia  with  this  matrix  and  trachyte 
fragments  will  be  a  "  siliceous  "  trachyte  breccia,  etc. 

(b)  Calcareous.     A   conglomerate   with   this   matrix   and 
diabase  fragments  will  be  a  "  calcareous  "  diabase  conglom- 
erate. 

(c)  Argillaceous.     This  will  furnish    "  argillaceous  "  lime- 
stone conglomerate,  etc. 

(d}  Ferruginous.  This  will  give  "  ferruginous "  quartz 
conglomerate,  etc. 

GLACIAL  AGGREGATES. 
I.  MEGACLASTIC. 

There  is  but  one  group  under  this  head  where  all  the 
fragments  are  of  large  size,  and  that  is  of 

ERRATICS,  Perched  Blocks. 

Large  masses  of  rock  moved  from  their  original  position 
by  a  glacier,  and  left  by  its  ablation  scattered  over 
mountain  and  valley  along  the  line  of  its  motion. 

These  are  found  abundantly  over  New  England,  and  the 
upper  tier  of  the  middle  and  western-central  States.  In  some 
places  they  are  as  large  as  a  house,  and  are  left,  in  many 


SECONDARY  ROCKS.  28 1 

cases,  so  delicately  poised  on  top  of  other  rocks  (on  which 
they  are  ''perched")  that  they  can  be  moved  by  the  hand. 
They  can  be  distinguished  from  the  country-rock  by  their 
difference  in  composition.  In  the  preceding  pages  notes 
have  been  made  of  the  occurrence  of  varieties  of  rocks  as 
"  bowlders,"  "  blocks,"  etc.,  of  this  origin. 

II.  MIXED  Glacial  Aggregates. 

The  majority  of  glacial  deposits  due  to  ice  alone  are 
found  under  this  head  ;  the  distinguishing  characteristic 
being  a  heterogeneous  unstratified  mixture  of  all  sizes  of 
material  from  the  finest  rock-meal  to  fragments  as  large  as 
a  house.  This  is  generally  termed  moraine-stuff,  and  it  can 
be  separated  according  to  its  origin  and  mode  of  formation 
into : 

i.  Lateral  Moraine-stuff.  This  was  originally  a  "  cliff  "  or 
"  slope  agglomerate  "  which  had  settled  on  the  side  of  the 
moving  glacier,  and  was  transported  with  little  or  no  abra- 
sion ;  so  that  its  particles  are  as  angular  as  when  they  reached 
the  ice.  In  the  event  of  the  stagnation  and  ablation  of  the 
ice  this  fringing  string  of  material  will  rest  along  the  flanks 
of  the  mountain  or  across  the  valley  where  the  edge  of  the 
ice  formerly  existed,  and  it  can  only  be  told  from  local  cliff- 
or  slope-agglomerates  by  the  finding  of  rocks  moved  out  of 
place,  as  sandstone  resting  on  granite,  granite  on  limestone, 
uniformly  red  rocks  resting  on  uniformly  white  ones,  etc. 
In  a  valley  its  detection  is  easier.  If,  however,  the  material 
reach'ed  the  ice-front,  it  became  intermingled  with  the  ma- 
terial brought  in  and  under  the  ice.  Two  glacial  affluents 
meeting  in  the  central  glacier  would  have  their  adjacent 
lateral  moraines  unite  in  a  medial  moraine,  which,  under 
similar  circumstances,  would  be  found  along  or  across  the 
valleys  traversed  by  the  ice,  and  parallel  to  the  lateral 
moraines. 


282  MANUAL    OF  LITHOLOG  Y. 

2.  Ground  Moraine.     This  material  is  formed  under  the 
glacier  by  the  grinding-  effect  of  the  rocks  frozen  into  its 
lower  portion  on  the  surfaces  traversed.     The  result  is  the 
grooving  and  polishing  of  both  rocks  and  surface,  and  the 
formation  of  "  rock-meal."     The  ablation  of  the  ice  leaves 
this  as  the  lowest  of  the  glacial  formations,  and  on  this  falls 
whatever  is  carried  in  or  on  the  ice.     This  is  also  called  sub- 
glacial  moraine.     It  usually  has  a  cement  of  dense  clay  or 
rock-meal  that  incloses  rounded    and  glaciated  fragments 
torn  from  outcrops  covered  by  the  flow  of  the  ice.     In  case 
the  fragments  are  unequiaxial  they  are  arranged  with  their 
longer  axes  parallel  to  the  motion  of  the  glacier.    Like  the  lat- 
eral stuff,  it  is  unstratified  and  quite  compact  from  the  press- 
ure of  the  mass  of  ice.     This  is  also  called  "  bowlder  clay." 

3.  Terminal  Moraine.    This  is  the  heterogeneous  material 
brought  in  any  way  by  the  glacier  and  heaped  at  its  front. 
It  contains  all  the  material  described  above,  and  in  some 
cases  forms  a  hill  more  than  100  feet  high  and  over  a  mile 
wide.     For  a  description  of  the  great  terminal  moraine  of 
the  Glacial  period  see  the  works  of  Lewis,  Wright,  Chamber- 
lain, Salisbury,  and  others.      (Kames,  drumlins,  etc.,  belong 
to  geology,  and- not  lithology.) 

III.  MEDIUM  to  MICROCLASTIC  Glacial  Aggre- 
gates. 

These  are  caused  by  the  ablation  of  the  ice.  It  can  melt 
under  two  general  conditions :  on  a  surface  that  will  allow 
ready  discharge  of  the  water,  or  against  a  slope  that  will 
hold  it  in  a  body  of  varying  dimensions ;  or,  again,  it  can 
reach  the  sea  or  a  lake,  and  "  calve  "  its  bergs  upon  the 
surface  with  their  burden  of  material.  The  two  last  cases 
are  practically  the  same,  if  we  eliminate  the  distributing 
effect  of  tides ;  but  with  tides  or  currents  the  results  are 
quite  similar.  We  distinguish: 


SECONDARY  ROCKS.  283 

1.  Aprons,  where  the  ablation  is  above  water,  and  where 
the  water  from  the  melting  ice  flows  away  with  its  burden 
down  a  slight  slope.     The  large  fragments  remain  at  the 
ice-front;  but  the  smaller  are  distributed  in  a  succession  of 
increments  that  produce  stratification  in  case  the  flows  vary, 
or  an  unstratified  aggregate  if  they  remain  constant.     This 
gradually  thins  out  on  going  away  from   the  ice-front,  and 
passes  from  coarse  to  fine  material,  and  finally  dies  out.    The 
characteristic  of  this  formation  is  the  uniformity  of  the  mass 
on  a  vertical  section. 

2.  Slack-water  Clay.     This  is  formed  by  the  discharge  of 
the    sub-glacial  streams  into  a   lake  or  quiet   sea,  so   that 
the  burden  of  fine  rock-meal  is  distributed  over  the  bottom, 
to  form  a  deposit  of  extreme  fineness  at  a  distance  from  the 
front,  but  becoming  more  sandy  and  gravely  near  it.     The 
bergs  from  the  ice-front  sail  away  with  their  burden  of  the 
varying  kinds  of  moraine-stuff  described,  and,  as  they  melt, 
they    drop    into    the    water   their   clay,    sand,    gravel,   and 
bowlders.     These  in  their  descent  arrange  themselves  so  as 
to  offer  the  least  resistance  to  the  water,  and  enter  the  clay 
at  all  angles ;  so  that  we  can  readily  distinguish  this  forma- 
tion from  the  "  bowlder  clay  "  or  "till  "-by  the  want   of 
arrangement  of  the  burden,  as  well  as  by  the  looser  state  of 
.aggregation,    there    being   no   ice-pressure    to    consolidate. 
The  Packer  clay  of  the  Lehigh  Valley,  Pa.,  of  this  formation, 
and  during  the  earliest  of  the  ice  advances,  is  in  some  cases 
Jifteen  feet  thick. 

PYROGENIC  AGGREGATES. 

(A)  PYROCLASTS. 

Fragments  formed  in  any  way  during  any  portion  of  an 
eruption,  and  remaining  loose  or  cemented  by  the 
eruptive  magma. 


284  MANUAL    OF  LITHOLOGY. 

These  fragments  may  be  taken  from  the  country-rock  in 
which  the  fissure  was  made,  from  the  eruptive  rock  itself, 
or  from  any  other  eruptive  rock.  According  to  their  state 
of  aggregation,  we  can  distinguish  : 

1.  Loose  Aggregates,  where   the  fragments  after   ejec- 
tion have  fallen  in  loose  masses  and  have  not  been  cemented 
by  any  medium.     According  to  their  size,  we  find  : 

(a)  Blocks.     Large  and  generally  solid  masses  (sometimes 
eight  feet  in  diameter)  ejected  from  volcanoes.     Sometimes 
these  are  compact  inside  and  slaggy  outside,  as  if  torn  from 
the  walls  and  partly  fused  ;  generally  they  are  angular  or 
subangular,  and  if  round  become  bombs. 

(b)  Bombs,    where    the    fragments    are   of  considerable 
size,  and  have  been  somewhat  fused  and  rounded  before 
ejection,  or  during  their  ejection,  from  their  plasticity  and 
the  rotatory  motion  to  which  they  were  subjected.     Promi- 
nent among  these  are  the  "  basaltic "  bombs  noted  in  the 
treatment  of  primary  rocks,  which  consist  almost  wholly  of 
olivine  or  a  mixture  in  which  it  is  predominant.     Stelzner 
reports  obsidian  bombs  from  Australian  volcanoes  i£  inches 
in  diameter.     Masses  of  slag  as  large  as  the  head  have  been 
discharged  from  Vesuvius  during  an  eruption. 

(c)  Lapilli.     Fragments  of  slag  as  large  as  a  walnut,  and 
thence  to  minute  sizes,  and  of  various  shapes.     They  are 
portions  of  the  vesicular  mass  blown  up  by  the  force  of 
eruption,  and  exhibit  a  vesicular  structure  within. 

(d)  Ash,  Sand,  when  smaller  than  lapilli.     It  consists  of 
the  finest  dust,  as  well  as  megascopic  sizes,  and  (m)  shows 
microliths,  glass  fragments,  and  minute  crystals.     The  sand 
is  coarser  than  the  ash,  and  the  series  from  coarse  to  fine 
would  read  :  blocks,  bombs,  lapilli,  sand,  and  ash.    Pozzulana 
is  a  loosely  coherent  sand  useful  for  hydraulic  mortar. 

2.  Pyroclastic    Breccias,  Friction     Breccias    (in    part). 
These  can  be  divided  according  to  the  origin  of  the  frag- 


SECONDARY  ROCKS.  28$ 

merits  included,  but  the  matrix  in  every  case  is  eruptive. 
These  breccias  can  be  distinguished  from  ordinary  ones  by 
the  matrix,  as  in  the  former  the  result  of  aqueous  action  is 
here  replaced  by  that  of  fire.  The  breccias  are  named  by 
stating-  both  fragments  and  matrix,  as  before  noted,  with  the 
exception  that  the  fragments  of  a  rock  cemented  by  a 
matrix  of  the  same  are  distinguished  from  the  similar  breccia 
formed  by  water  by  prefixing  "  pyroclastic  "  (see  under  (b\ 
below).  The  varieties  are : 

(a)  Where  the  country-rock  is  different  from  the  eruptive 
magma.     Here  fragments  of  phyllite  or  sandstone  cemented 
by   eruptive    basalt    would   be     "  phyllite-basalt "  breccia, 
•"  sandstone-basalt "  breccia.     In   the   same   way  we  would 
have  "  granite-quartz-porphyry  "  breccia,  etc. 

(b)  Where  the  first  outrush  of  the  magma  had  its  selvages 
chilled  against  the  walls,  and  portions  of  these  are  torn  off 
by  the  following  rush  and  solidified  with  it.     Here  frag- 
ments and  magma  are  alike,  and  we  would  have  a  "  quartz- 
porphyry-quartz-porphyry  "  breccia,   or,   briefly,   as  stated 
above,  a  "  pyroclastic  quartz-porphyry  "  breccia,  in  distinc- 
tion from  a  "  quartz-porphyry  "  breccia  formed  from  debris. 

(c)  Where  the  same  or  previous  eruptions  have  formed  a 
•cone  of  vesicular  lava,  lapilli,  etc.,  and  subsequent  extrusions 
have  filled  the  crater  and  burst  through  the  walls  to  form  a 
breccia  with  the  cinders,  lapilli,  etc.     In  this  case  the  name 
would  be  as  in  the  last,  but  the  character  of  the  breccia 
would  be  different,  as  the  fragments  would  be  more  vesicular. 

(ff)  TUFFS. 

Aggregates  of  volcanic  ejectamenta  of  varying  size,  more 
or  less  firmly  compacted  by  the  agency  of  water,  and 
therefore  more  or  less  weathered. 

These  ejectamenta  are  the  blocks,  bombs,  lapilli,  sands,  and 
ashes  just  described.     On  being  thrown  into  the   air  they 


286  MANUAL    OF  LITHOLOGY. 

fall  at  distances  from  the  volcano  dependent  on  the  force 
and  direction  of  discharge  and  the  velocity  of  the  wind,, 
which  sorts  the  material,  and  carries  the  particles  to  dis- 
tances dependent  on  their  fineness.  The  classic  eruption  of 
Krakatoa  sent  its  fine  dusts  50,000  feet  into  the  air,  so  that 
they  encircled  the  globe,  and  remained  suspended  long 
enough  to  produce  the  peculiar  appearances  at  sunset  dur- 
ing the  following  autumn.  An  examination  of  the  deep-sea 
deposits  shows  us  that  volcanic  ashes  are  distributed  every- 
where. This  sorting  causes  a  gradual  transition  from  the 
coarse  material  at  the  foot  of  the  volcano  to  the  finest  mate- 
rial  at  a  distance,  with  a  corresponding  diminution  in  amount 
of  sediment,  and  a  corresponding  increase  in  the  proportion- 
of  foreign  admixtures.  The  ejectarnenta  may  fall  under  two- 
general  conditions :  on  land  or  into  water.  Falling  on 
land  they  may  accumulate  as  a  dry,  loose  dust,  or  may  be- 
come mixed  with  the  condensed  moisture  that  follows  an 
eruption,  and  fall  to  the  earth  as  a  muddy  rain,  which  will 
accumulate  as  a  flow  of  mud  that  covers  the  low  lands  at 
the  mountain  foot,  as  was  the  case  with  Pompeii.  The  dry 
dusts  remain  until  a  heavy  rain  or  the  melting  of  deep  snows 
forms  with  them  a  thin  mud  which  flows  in  a  similar  man- 
ner, but,  in  this  case,  bears  with  it  whatever  may  have  accu- 
mulated on  the  surface  during  or  since  the  deposit  ol  the 
dust,  such  as  portions  of  vegetation,  etc.  In  either  case 
these  flows  form  regular  strata  and  exhibit  a  "  pseudo- 
fluidal"  structure  (the  migration  structure  of  Giimbel),  and  a 
section  will  exhibit  compact,  sandy,  conglomerated,  and 
brecciated  states,  with  inclusions  of  foreign  organic  and  in- 
organic material  (leaves,  stems,  trunks,  pebbles,  etc.).  In 
case  the  volcano  be  near  a  lake  or  the  sea  the  ejectamenta 
will  form  a  uniformly  pure  stratified  deposit  on  and  below 
the  adjacent  shore,  and  this  will  become  intermixed  with 
foreign  sediment  at  greater  distances,  so  as  to  form  a  gradual 


SECONDARY  ROCKS.  28/ 

transition  from  tuff  to  sediment,  and  both  would  inclose  fos- 
sils of  the  period.  Miigge  proposes  the  term  tuffite  for 
automorphic  tuff  sediments,  and  tuffoid  for  similar  regional 
metamorphic  sediments  (provided  that  it  is  regional  and  not 
contact  metamorphism).  Weathered  tuffs  resemble,  when 
of  fine  grain,  weathered  debris  in  place,  but  a  distinction 
can  be  made,  as  with  tuffs  foreign  inclusions  just  noted,  and 
bombs,  lapilli,  etc.,  are  the  rule ;  with  debris  in  place,  the 
exception.  Laterites  form  from  tuffs  as  from  rock  in  place, 
and  through  the  same  causes.  As  tuffs  are  peculiar  to  vol- 
canic rocks,  their  association  with  old  eruptives,  which  are 
now  known  as  intrusives,  proves  that  they  reached  the  sur- 
face, and  that  their  surface  deposits  were  similar  to  those  of 
active  volcanoes.  Separating  these  into  tuff,  tujfite,  and 
tuffoid,  the  following  varieties  have  been  noted : 

I.  TUFF. 

Accumulations  of  volcanic  ejectamenta  on  land,  more  or 
less  solidified  by  rain  and  surface  water. 

(a)  Quartz-porpkyry-tuft,  Porphyry-tuff,  Felsite-tuff,  Feld- 
spathic  Ash  (Jukes).     An  earthy,  clayey,  and  usually   com- 
pact "  claystone,"  colored  from  snow-white  through  shades 
of   yellow  and  green  to   brown  and   bluish,  and  inclosing 
crystals   of    quartz   and    mica,   and    fragments    of    organic 
bodies.      Silica   75-80 ;    Gr.    2.62-3.02.      Found    in   Alsace, 
Saxony,  China,  and  abundantly  in  Wales.     It  passes  over 
into  the  debris  conglomerates  and  breccias  of  the  rock. 

(b)  Rhyolite-tuft.  is  abundant  in  Hungary  and  Nevada. 

(c)  Rhyolite-perlite-tuft  is  found  with  rhyolite-tuff. 

(d)  Rhyo lite-pumice-tuft    is    extensively    developed    with 
rhyolitic  extrusions. 

(e)  Trachyte-iuft.  occurs  as  a  fine   earthy   mass  of  light 
colors  in  Hungary,  Italy,  and  other  trachyte  regions,  and 


288  MANUAL    OF  LITHOLOGY. 

carries  impressions  of  plants,  etc.,  and  as  secondary  products 
wood-  and  precious  opal. 

(f)  Trass  (Rhine),  Pausilippo  (Sicily),  Tosca  (Teneriffe), 
Moja  (South  America),  are  tuffs  formed  from  mud-streams 
due  to  rain  and  melting-  snow,  and  contain  a  high  content 
of  foreign  inclusions.  They  are  all  rhyolitic  or  trachytic  in 
their  composition,  and  are  local  names  of  the  same  forma- 
tion. 

(«£")  PhonoKte4.\&  is  found  in  France,  Bohemia,  etc.,  near 
the  phonolite  extrusions,  and  /?#«te-phonolite-tuff  occurs  at 
the  lake  of  Laach. 

(h)  Andesite-\.\&§.     From  Santorin,  the  Andes,  etc. 

(i)  Mica-porphyrite-\.\&  is  reported  from  Italy. 

(/)  Diorite-tuft,  or  what  seems  to  be  such,  is  reported  in 
one  extended  locality  near  Badmannsdorf. 

(k)  Basalt-\.\&.  This  is  a  dirty  gray  to  yellowish  brown 
aggregate  of  small  particles  of  basalt.  It  is  full  of  the 
alteration  products  from  basalt — green  earth,  calcite,  zeo- 
lites, etc.,  and  is  extensively  developed  in  basaltic  regions. 

(I)  Peperino  is  an  ash-gray  tuff  from  the  Alban  Hills  of 
Italy.  The  grayish  matrix  incloses  folia  of  black  mica, 
grains  and  phenocrysts  of  augite,  leucite,  and  magnetite, 
with  fresh  and  weathered  olivine. 

(m)  Palagonite-\u&  (v.  Waltershausen).  First  noted  at  Pala- 
gonia,  Sicily.  It  is  a  glassy  basalt  with  much  included 
water,  and  is  caused  by  the  action  of  hot  water  on  the 
molten  rock.  Some  authorities  describe  the  rock  as  due  to 
a  discharge  under  water.  It  is  compact  and  amorphous, 
with  pitchy  luster ;  color  yellow  to  black  ;  conchoidal  to 
splintery  fracture;  H.  4.5;  Gr.  2.4-2.6,  and  chemical  com- 
position of  basalt.  The  action  of  the  water  has  con- 
verted all  the  iron  present  as  protoxide  to  sesquioxide. 
Rosenbusch  has  found  that  the  interior  of  the  palagonite 
fragments,  which  the  original  investigator  named  siderome- 


SECONDARY  ROCKS.  289 

lane,  is  a  highly  ferruginous  and  waterless  tachylite.  Palag- 
onite  is  found  extensively  in  Iceland,  and  with  it  hyalome- 
/a  tie-tuft. 

(n)  Mefapkyre-toS.  is  reported  from  Germany  and  Greece. 

(o)  Augite-porphyrite-\.\&  is  reported  from  the  Tyrol  and 
elsewhere. 

(p)  Dia&ase-tuR  is  extensively  developed  in  the  Voigt- 
land,  Harz,  England,  etc. ;  of  gray  to  brownish  green 
color. 

All  of  the  above  rocks  are  characterized  by  the  presence 
of  inclusions  that  point  to  an  origin  on  land.  In  1861 
v.  Richthofen  was  the  first  to  attempt  to  separate  tuffs 
according  to  their  manner  of  deposition  and  subsequent 
treatment ;  but  Miigge,  as  stated  above,  was  the  first  to 
propose  names  for  the  varieties  formed  under  water  and 
afterwards  metamorphosed,  as : 

II.  TUFFITE  (Miigge). 

A  tuff  that  has  accumulated  under  water  and  has  inclu- 
sions of  marine  life,  but  which  has  been  consolidated 
by  pressure  alone,  and  has  not  undergone  "  meta- 
morphism." 

Not  very  many  types  of  this  rock  have,  thus  far,  been 
reported,  as  the  majority  of  observers  have  directed  their 
attention  elsewhere,  and  it  is  by  no  means  the  most  easy 
matter  to  form  the  necessary  distinction  without  the  exami- 
nation of  a  considerable  area.  Tuffites  of  quartz-porphyry 
are  reported  from  Wales,  of  augite-porphyrite  from  the 
Tyrol,  and  the  following  rock  is  probably  of  this  group  : 

Pietra  Verde.  This  is  found  in  Italy,  southern  Tyrol,  the 
Balkans,  etc.  It  is  a  rock  like  hornstone,  with  silica  50-69 ; 
Gr.  3  ;  colored  green  to  dark-green,  and  splintery  fracture. 
It  can  just  be  scratched  by  steel,  and  is  found  among  the 
Mesozoic  sediments  of  the  southern  Alps. 


2QO  MANUAL   OF  LITHOLOGY. 

III.  TUFFOID  (Miigge). 

A  tuff  or  tuffite  altered  by  regional  metamorphism. 

This  can  only  be  told  from  the  foregoing  by  the  micro- 
scope in  hand  specimens ;  but  in  the  field  it  will  be  found 
associated  with  metamorphic  rather  than  sedimentary  rocks* 
Under  this  seem  to  fall 

(a)  Schalstein.  This  is  a  metamorphosed  diabase-tuffite, 
and  is  found  extensively  developed  in  Nassau,  Devonshire, 
etc.  Silica  17-44;  Gr.  2.63-2.85.  The  base  looks  like  a 
diabase-tuff ;  but  it  is  mottled  with  greenish,  gray,  and 
spotted  layers  of  calcite.  It  is  sometimes  amygdaloidal,  and 
sometimes  contains  brecciated  fragments  of  argillite  and 
chlorite-schist. 

(U)  G^^-schalstein  is  reported  from  the  upper  island 
of  Japan  (Hokkaido). 

IV.  SILICIFIED  Tuffs,  Breccias,  etc. 

Tuffs,   etc.,  with   their  original   materials  replaced   by 
.    silica. 

These  are  rare  occurrences,  and  have  thus  far  been  re- 
ported from  the  Black  "Forest,  Odenwald,  in  Europe;  Sau- 
gus,  Mass.,  where  quartz-porphyries  have  been  thus  far 
found  in  this  state,  and  in  the  Sudbury  district  of  Canada 
in  a  band  of  silicified  breccia  more  than  forty  miles  wide. 

OROCLASTIC  (CATACLASTIC)  BRECCIAS. 

These  rocks  have  been  formed  on  immense  scales  by  the 
crushing  of  rocks  during  orogenic  movements.  They  can 
be  divided  into  two  general  classes : 

I.   SHEAR-ZONE  Breccias,    Friction    Breccias  (in 
part). 


SECONDARY  ROCKS. 

Breccias  produced  by  crushing  of  rocks  along  fractures, 
either  directly  or  aided  by  a  lateral  movement,  and 
cemented  by  the  comminuted  portions  formed  during 
the  movement,  and  washed  into  the  interstices;  or  by 
infiltration  of  aqueous  solutions,  either  with  or  with- 
out metamorphism  of  a  slight  character  produced 
by  the  heat  developed  during  the  shear. 

In  many  cases,  as  along  the  shores  of  Avalanche  Lake,  N. 
Y.,  the  rock  of  the  shear-zone  has  been  metamorphosed ;  but 
where  the  fragments  retain  their  angularity,  the  class  can 
be  distinguished  from  other  breccias,  as  follows : 

From  pyrogenous  breccias  of  the  walls  of  the  country- 
rock  by  the  nature  of  the  matrix,  which  is  eruptive  in  the 
latter  and  aqueous  in  the  former. 

From  pyrogenous  breccias  of  the  tuff  type  by  the  dif- 
ferences in  the  included  fragments. 

From  debris  breccias  by  the  greater  angularity  of  the 
fragments. 

From  stratified  breccias  by  the  absence  of  sand  and 
gravel  and  the  general  uniformity  of  the  fragments. 

II.  REGIONAL  Breccias. 

Breccias  produced  by  the  crushing  of  extensive  areas  of 
the  solid  rocks  during  orogenic  movements,  with  little 
or  no  displacement  of  the  crushed  portions,  and  a 
cementing  by  infiltration  of  aqueous  solutions,  and 
generally  of  a  calcareous  or  siliceous  nature. 

These  are  found  bordering  the  regions  of  mountain  ele- 
vation. A  good  example  is  seen  in  the  Siluro-Cambrian  sandy 
limestone  of  eastern  Pennsylvania,  along  the  north  flank  of  the 
South  Mountain,  as  it  exhibits  large  areas  of  rock  crushed 
into  fragments  of  all  sizes,  which  have  not  moved  from  their 
places,  and  retain  their  lines  of  sedimentation,  but  which  have 


292  MANUAL    OF  LITHOLOGY. 

been  firmly  cemented  by  calcite  infiltrations.  The  spaces  be- 
tween the  fragments  are  usually  thinner  than  a  sheet  of  writ- 
ing-paper, and  the  contrast  between  the  various  colors  and 
textures  of  the  limestone  and  its  white  cement  is  strong. 

AUTOMORPHIC    CHEMICAL   AGGREGATES. 

These  are  the  results  of  the  solution  of  minerals  and  their 
deposition  by  the  drying  or  cooling  of  the  liquid.  The  sol- 
vents are  waters  charged  with  various  acids  and  of  varying 
temperatures.  The  theories  of  the  formation  of  these  de- 
posits belong  to  geology  ;  the  results  can  be  grouped  under 
two  heads. 

I.  Aggregates  from  drying  or  oxidation. 

II.  Aggregates  from  cooling  or  saturation. 

1.  This  class  of  deposits  is  by  far  the  greater  in  number 
of  species  and  extent  of  formations.  The  process  has  been 
going  on  since  the  beginning  of  the  accumulation  of  water 
on  the  earth's  surface.  The  materials  held  in  solution  are 
various  ;  but  the  bulk  of  the  deposits  are  found  to  belong  to 
these  groups. 

i.  Calcareous;  2.  Haloidal ;  3.  Ferruginous;  4.  Aqueous. 

CALCAREOUS  DEPOSITS. 

These  are  mainly  of  two  salts,  the  carbonates  and  the 
sulphates.  Under  the  former  are  the  limestones  deposited 
during  early  times  ;  but  as  these  cannot  be  now  told  from 
highly  metamorphosed  later  sediments,  there  will  be  no  at- 
tempt to  separate  the  two  forms.  The  other  form  of  lime- 
stone is  shown  in  stalagmite  and  stalactite,  formed  at  the 
(present  day  wherever  caverns  exist.  The  sulphates  are  due 
to  the  drying  of  saline  solutions  and  the  deposit  of  the  lime 
:salts  at  an  early  period,  as  the  solubility  of  gypsum  is  very 
slight. 


SECONDARY  ROCKS.  2$$ 

(a)  STALACTITE  and  STALAGMITE. 

Stalactites  are  formations  found  on  the  roofs  of  caverns 
or  other  places  composed  of  limestone,  or  containing  lime- 
stone, as  on  the  under  sides  of  bridge-arches  of  limestone, 
or  even  of  sandstone  cemented  with  ordinary  mortar.  They 
resemble  icicles,  and  are  caused  by  the  percolating  water 
running  preferably  down  certain  spots  with  not  too  high 
velocity,  The  dropping  water  loses  its  carbonic  acid  and 
also  dries,  so  that  its  soluble  salts  are  added  to  the  icicle-like 
form,  and  it  increases  in  length  till  it  sometimes,  as  in  the 
Mammoth  and  other  caves  reaches  many  feet.  The  stalag- 
mite is  formed  underneath  the  stalactite,  where  the  drops 
have  reached  the  floor,  and  is  an  icicle  reversed,  and  growing 
upwards.  The  terms  do  not  presuppose  that  the  material  is 
carbonate  of  lime,  as  stalagmites  and  stalactites  are  found  in 
similar  positions  and  formed  of  fluorite,  barite,  chalcedony, 
limonite,  etc.,  and  only  the  form  of  the  deposit  is  indicated  ; 
but,  as  they  are  found  of  this  composition  many  times  more 
abundantly  than  of  all  the  others  combined,  the  terms  without 
other  limitations'  are  usually  referred  to  formations  of  lime. 
A  section  of  either  shows  concentric  rings,  formed  by  dis- 
tinct layers  of  material,  which  sometimes  vary  considerably 
in  color. 

(b)  GYPSUM. 

An  aggregate  of  hydrous  sulphate  of  lime ;  usually 
crystalline ;  sometimes  compact  or  fibrous ;  white 
when  pure,  but  gray,  yellow,  brown,  and  red  when 
impure. 

Gr.  2.32  ;  H.  1.5-2. 

Its  softness,  high  content  of  water,  and  sulphur  reaction 
distinguish  \it  from  similar-appearing  rocks.  The  gray 
varieties  are  contaminated  with  bitumen,  and  the  other  colors 
are  due  to  iron.  As  accessories  occur  pyrite,  chalcopyrite, 


294  MANUAL    OF  LITHOLOGY. 

quartz,  mica,  boracite,  sphalerite,  galena,  halite,  dolomite, 
sulphur,  and  other  minerals  to  a  less  degree.  Alabaster  is 
a  white,  granular  gypsum,  sometimes  semitranslucent. 

(c)  ANHYDRITE. 

An  aggregate  of  anhydrous  sulphate  of  lime. 
Gr.  2.8-3  :   H.  3-3.5- 

This  is  told  from  calcite  and  dolomite  by  its  failure  to 
effervesce  with  acids,  and  from  gypsum  by  its  absence  of 
water.  It  occurs  with  gypsum. 

Both  of  these  occur  with  beds  of  rock  salt  in  lenticular 
masses.  They  occur  to  great  thickness  (600  feet)  in  the 
United  States,  and  gypsum  is  mined  in  Michigan,  Kansas, 
New  York,  Iowa,  Virginia,  Ohio,  Utah,  Colorado,  California, 
Wyoming,  South  Dakota  and  Texas.  From  Utah  come  crys- 
tals of  gypsum  weighing  hundreds  of  pounds.  An  alterna- 
tion of  light  and  dark  layers  of  gypsum  is  called  tripestone. 

HALO  I  DAL  AGGREGATES. 
ROCK-SALT. 

An  aggregate  of  chloride  of  sodium  ;  when  pure,  per- 
fectly transparent  and  clear  as  water ;  variously  col- 
ored by  impurities  ;  crystalline,  fibrous,  granular, 
foliated. 

Gr.  2.1-2.2. 

As  a  rock,  salt  is  usually  impure  from  gypsum,  chlorides 
of  lime  and  magnesia,  clay,  etc.  The  thickest  beds  of  the 
world  are  at  Stassfurt  (1800  feet)  and  Sperenberg,  near 
Berlin  (3600  feet).  In  the  United  States  rock-salt  is  found 
at  the  island  of  Petit  Anse,  La. ;  in  the  region  of  Wyoming, 
Genessee,  and  Livingston  counties,  N.  Y. ;  and  in  Kan- 
sas, Nevada,  Utah,  and  California.  As  salt-marls  it  is 
found  in  the  Salina  formation  through  New  York,  Ohio, 


SECONDARY  ROCKS. 

Indiana,  Michigan,  and  western  Ontario.  The  salt  lakes  of 
the  United  States  are  noted — especially  the  Great  Salt 
Lake  of  Utah,  which  is  75  miles  long  by  40  wide.  Other 
lakes  occur  in  Utah,  Nevada,  California,  and  Texas  with 
salt-formations  in  their  vicinity. 

CARNALLITE. 

An  aggregate  of  chloride  of  potassium  and  magnesium 
with  conchoidal  fracture  and  red  color. 
Gr.  1.6. 

In  a  bed  at  Stassfurt  100  feet  thick  overlying  the  salt, 
and  associated  with  it  at  other  places. 

FLUORITE,  Fluor  Spar. 

A  crystalline — rarely  compact — aggregate  of  fluoride  of 
calcium. 

Gr.  3.1-3.2;  H.  4. 

This  occurs  in  beds  in  a  few  cases  ;  generally  in  veins  in 
gneiss,  mica-schist,  clay-slate,  both  crystalline  and  uncrys- 
talline  limestones,  and  in  sandstones.  It  is  often  the  gangue 
of  metallic  ores.  It  occurs  in  Cumberland  and  Derbyshire, 
England,  Saxony,  Norway,  and  Baden.  In  the  United 
States  it  is  found  in  the  adjacent  counties  of  Pope  and 
Harden  in  Illinois,  and  Livingston,  Crittenden,  and  Cald- 
well,  Ky.,  where  it  occurs  as  a  vein  associated  with  galena 
and  other  minerals. 

CRYOLITE. 

A  coarse-grained   and   thick-bedded   aggregate   of  the 
fluorides  of  sodium  and  aluminium. 
Gr.  2.95  ;  H.  2.5-3. 

This  occurs  in  a  huge  bed  overlaid  by  granite  at  Ivigtut, 
Greenland,  in  snow-white  masses  partially  transparent  and 


296  MANUAL    OF  LITHOLOGY. 

with  vitreous  luster.  It  is  open-worked,  and  the  opening  in 
1892  was  600  feet  long  and  200  feet  wide  and  over  185  feet 
deep. 

FERRUGINOUS  AGGREGATES. 
IRON   ORES. 

As  the  majority  of  these  have  been  subjected  to  meta- 
mo'rphism,  and  all  cannot  be  grouped  under  this  head  as  far 
as  origin  is  concerned,  they  will  be  treated  under  the  head 
of  "  Minerals  as  Rocks."  In  this  place  it  will  be  only  noted 
that  siderite  is  deposited  as  carbonate,  and  in  many  cases  is 
intimately  mixed  with  limestones  and  dolomites.  The  spots 
of  iron  soon  become  oxidized  and  are  deposited  as  hydrated 
sesquioxide  mud  with  other  sediments,  or  accumulate  in 
shallow  ponds  near  the  sea  or  lakes,  and  form  lenticular 
masses  of  limonite.  These  by  loss  of  water  become  hema- 
tite, or,  by  partial  reduction  through  organic  aggregates, 
become  magnetic  oxides.  At  any  rate,  the  ores  as  a  body 
are  held  to  have  an  origin  as  given,  and  some  authorities 
state  that  it  is  the  sole  origin.  In  the  first  part  of  this  book 
(under  "  Gabbro")  the  ideas  of  other  authorities  were  given 
that  the  primal  source  of  the  iron  was  through  igneous  in- 
jections and  extrusions  from  abyssal  sources. 

AQUEOUS  AGGREGATES. 
ICE. 

An   aggregate   of   frozen   (crystalline)  water,  granular, 
compact,  schistose. 

It  may  be  formed  by  the  solidification  of  the  atmospheric 
moisture,  as  snow,  and  thence  compressed  to  ice ;  or  it  may 
form  on  the  surface  of  water  immediately.  We  can  distin- 
guish : 

(a)  Ndvt,  Oolitic  Ice.  A  granular  aggregate  of  ice 
formed  on  the  tops  of  peaks,  where  there  is  a  considerable 


SECONDARY  ROCKS. 

variation  in  temperature,  by  the  rounding  of  the  individual 
grains  of  crystalline  snow  and  their  gradual  aggregation  to 
form  the  oolitic  grains  of  the  ne've'  t or  firn,  as  it  is  called. 

(b)  Glacier  Ice.     A  consolidated    neve   by   compression 
and  the  infiltration  of  water,  as  the  ne"v£  slides  down  the 
sides  of  the  hills.     The  interior  of  the  glacier  ice  is  crystal- 
line, in  distinction  from  the  granular  character  of  the  firn 
or  neve.     It  is  filled  with  air-bubbles  when  in  small  masses,, 
and  these  may  be  full  of  mud.     In  large  masses  it  is  fre- 
quently an  alternation  of  white  layers  full  of  vertical  air- 
bubbles  and  blue,  dense,  and  clear  layers. 

(c)  Water  Ice.     Formed   on  the   surface   of  water,   and 
compact ;  white  or  greenish.     It  may  be  formed  from  fresh 
or  salt  water. 

(d)  Ground  Ice.     This  is  where  shallow  water  freezes  to 
the  bottom,  and  thus  incloses  the  stones  and  finer  material 
of  that  bottom.     It  sometimes  forms  in  deep  water  by  the 
freezing  of  the  lowest   layer  of   water   during  very  cold 
weather. 

AUTOMORPHIC  ORGANIC  AGGREGATES. 

I.  ZOOGENIC. 

Aggregates  produced   by  animal  agency,  and  accumulated  me- 
chanically by  any  of  the  aeollan  or  aqueous  forces. 

II.  PHYTOGENIC. 

Aggregates  produced  by  vegetable  agency,  either  grown  in  place 
or  accumulated  as  above  stated. 

(A)   CALCAREOUS. 
i.  LIMESTONE  Group. 

A  compact  uncrystalline  aggregate  of  carbonate  of  lime  ; 
massive,  concretionary,  earthy,  or  hypocrystalline  ; 
colored  white,  whitish,  grayish,  bluish,  blue,  brown- 
ish, black  ;  usually  with  accessory  clay  or  sand,  or 
both.  Gr.  2.6-2.8  ;  H.  3. 


298  MANUAL   OF  LITHOLOG  Y. 

Here  will  be  classed  all  forms  of  limestone,  whether  of 
chemical  or  organic  origin,  as  already  stated.  Most  lime- 
stones are  of  organic  and  zoogenic  origin,  though  some  are 
phytogenic.  Chemical  and  zoogenic  limestones  will  be 
noted  together. 

I.  ZOOGENIC  SECTION. 
(a)  LIMESTONE. 

A  compact  rock  with  conchoidal  to  splintery  fracture ; 
dull ;  color  generally  gray  or  yellowish  blue,  green, 
red,  brown,  or  black. 

It  is  rare  that  pure  carbonate  of  lime  is  found  in  nature. 
The  iron  salts  give  the  rocks  red  colors;  carbonaceous  im- 
purities make  them  dark ;  clay  and  silica  alter  their  hard- 
ness and  change  them  from  ordinary  to  hydraulic  varieties. 
The  ordinary  limestones  are  compact,  especially  the  recent 
geological  ones  ;  the  older  ones  are  frequently  coarse-crys- 
talline. It  is  often  associated  and  mixed  with  magnesian 
limestone  (dolomite),  and  in  some  cases  the  fossils  will  be 
dolomite  and  the  inclosing  rock  calcite  (Hunt).  Limestone 
can  be  told  from  dolomite  by  its  lower  specific  gravity,  its 
greater  effervescence  with  acids,  and  its  action  when  pow- 
dered and  heated  on  platinum  foil  (limestone  powder  heat- 
ing quietly,  glowing,  and  adhering  together ;  dolomite 
powder  swelling  and  becoming  loose,  or  fusing  to  a  slag  if 
clayey).  Many  limestones  appear  to  be  compact  rocks  and 
non-fossiliferous  on  a  fresh  fracture,  but  on  exposure  to 
weathering  the  less  soluble  fossils  remain  (while  the  matrix 
decomposes),  and  thus  obtain  a  high  relief.  Other  limestones 
show  at  once  their  origin,  and  are  almost  entirely  composed 
of  fossils,  which  may  be  cemented  by  a  compact  matrix,  or 
may  be  loosely  held  together  by  porous  material  washed 
into  their  interstices.  Pure  limestone  contains  56  per  cent 


SECONDARY  ROCKS.  299 

of  lime.  When  metamorphosed,  limestone  becomes  marble 
(q.  v.).  The  inclusions  in  limestone  are  varied  and  numer- 
ous. The  fossils  are  generally  removed  in  the  older  rocks 
by  infiltrations  which  have  entirely  replaced  the  body  of  the 
fossil,  or  have  more  or  less  fully  filled  the  cavity  with  crys- 
tals of  different  minerals.  As  accessories  are  found  com- 
monly quartz,  mica,  pyrite,  lead,  sphalerite,  chalcopyrite, 
and  sulphur.  These  occur  sometimes  scattered  through  the 
mass,  but  usually  in  nests,  strings,  druses,  geodes,  etc.,  in 
the  cavities,  cracks,  etc.,  in  the  rock.  The  fact  that  lime- 
stone was  deposited  as  a  calcareous  mud  in  layers  has  al- 
lowed drying  and  consolidation  to  form  joint  planes  normal 
to  the  bedding  planes  ;  and  the  further  fact  that  it  is  readily 
soluble  in  water  charged  with  carbonic  acid  has  allowed  its 
ready  solution  and  etching  by  surface  waters,  which  have 
thus  hollowed  it  along  joint  and  bedding  planes,  to  form 
gashes  and  caverns  of  varying  sizes,  and  in  which  the  ac- 
cessory minerals — especially  the  ores  noted  above — could  be 
deposited.  Its  impregnation  by  solutions  of  magnesia  has 
produced  many  dolomites,  and  solutions  containing  sul- 
phuric acid  have  formed  some  gypsums  and  anhydrites. 
The  varieties  are : 

Dolomitic  Limestone.  This  is  a  porous  yellowish  to 
dark-gray  stone  with  considerable  carbonate  of  magnesia  in 
its  composition,  but  not  enough  to  make  a  pure  dolomite. 
Its  specific  gravity  is  higher  than  that  of  limestone  in  pro- 
portion to  the  amount  of  the  dolomitic  contamination.  It 
is  found  associated  with  limestone,  and  in  some  quarries  the 
infiltrating  solution  that  has  produced  the  dolomitization 
has  proceeded  irregularly  downwards,  so  that  portions  of  a 
stratum  are  limestone  and  other  adjacent  portions  contain 
magnesia.  In  the  Silurian  limestones  of  Pennsylvania 
alternate  layers  in  a  quarry  consist  of  pure  and  dolomitic 
limestone. 


300  MANUAL   OF  LITHOLOG  Y. 

Siliceous  Limestone.  This  may  have  the  silica  scat- 
tered throughout  the  mass  to  form  a  harder  stone,  or  it 
may  occur  in  nests,  strings,  etc.  It  sometimes  occurs  in 
nodules  of  chert  or  hornstone,  that  appear  after  slaking 
the  lime,  as  lumps  and  sands.  This  variety  is  called 
cherty  limestone.  It  is  common  in  the  Siluro-Cambrian 
limestones  of  eastern  Pennsylvania,  near  the  base  of  the 
measures. 

Bituminous  Limestone,  Fetid  Limestone,  Swinestone, 
Stinkstone.  This  is  generally  dark-colored,  and  emits  a 
bituminous  odor  when  struck,  heated,  or  rubbed.  Some 
stones  do  not  show  this  discoloration  when  fresh,  as  the 
limestone  of  northern  Illinois,  which  is  light-colored  when 
quarried,  but  after  exposure  to  air  and  dust  becomes 
mottled  with  blackish  patches.  On  treating  with  HC1  a 
scum  of  bitumen  is  left.  It  belongs  to  the  older  geological 
formations,  and  is  not  found  later  than  the  Lias. 

Argillaceous  Limestone,  Marly  Limestone,  Clayey 
Limestone.  A  usually  gray  rock  with  light-reddish  and 
yellowish  shades ;  of  dull  fracture — almost  earthy ;  some- 
times splintery ;  leaving  considerable  clay  after  treatment 
with  HC1.  Pyrite  is  abundant.  These  are  transitions 
between  limestone  and  marl,  and  are  found  on  the  border- 
lines between  calcareous  and  argillaceous  areas  of  sedi- 
ments. In  the  great  valley  between  the  Kitatinny  and 
South  mountains  in  eastern  Pennsylvania,  the  border  be- 
tween the  slates  of  the  north  and  the  limestones  of  the  south 
is  occupied  by  a  belt  of  argillaceous  limestone,  much  of 
which  is 

Hydraulic  Limestone.  This  contains  from  10  to  50  per 
cent  of  silica,  alumina,  and  iron  oxide ;  does  not  slake  at 
all  under  water,  or  at  least  very  slowly,  and  its  "  setting  " 
is  due  to  a  chemical  combination  of  lime  and  magnesia 
with  silica  and  alumina.  It  is  always  a  transition  between 


SECONDARY  ROCKS.  3OI 

a  calcareous  and  an  argillaceous  formation,  and  partakes 
of  the  characteristics  of  both,  being  fine-grained,  frequently 
cleavable,  with  greater  tendency  to  splintery  fracture 
(like  shale),  and  with  an  effervescence  to  show  its  calca- 
reous nature.  It  resembles  the  shales  more  than  the  lime- 
stones. 

Lithographic  Limestone  is  a  slightly  argillaceous  and 
siliceous  limestone,  with  an  eminently  uniform  and  fine 
grain ;  breaking  with  a  subconchoidal  fracture,  and  ex- 
hibiting, as  a  rule,  a  gray,  drab,  or  yellowish  color.  It 
must  be  porous  enough  to  absorb  the  greasy  compound 
which  holds  the  ink ;  soft  enough  to  work  under  the  en- 
graver's tool,  and  homogeneous  throughout ;  without  veins, 
nests,  cracks,  or  irregularities  or  impurities  of  any  kind, 
so  that  the  reagents  will  act  on  all  parts  with  equal  force. 
The  best  lithographic  limestone  is  at  Solenhofen,  Bavaria ; 
'but  stones  are  used  from  many  other  countries.  In  the 
United  States  it  has  been  reported  in  Arizona,  Alabama, 
Arkansas,  Indiana,  Illinois,  Iowa,  extensively  in  Kentucky, 
Missouri,  Tennessee,  Texas,  Utah,  and  Virginia ;  but  while 
small  pieces  may  be  found  at  these  localities,  the  value 
of  the  stone  is  its  possessing  the  above  requirements,  and 
its  formation  in  masses  of  sufficient  size.  The  Arizona 
stone  seems  to  promise  the  largest  and  most  uniform 
pieces. 

Sandy  Limestone  is  a  transition  between  sandstone  and 
limestone  which,  by  weathering,  leaves  the  sand  in  masses. 
This  is  common  in  the  transition  beds  between  the  Potsdam 
sandstone  and  the  Silurian  limestone  of  Pennsylvania,  and 
especially  in  Center  County,  where  the  weathering  of  the 
rock  has  left  great  depths  of  sand  over  the  "  sandy  barrens." 
The  fractured  surface  of  this  rock  feels  harsher  than  that  of 
limestone,  and  the  sand  is  left  as  a  sediment  on  treating 
with  HC1. 


3O2  MANUAL   OF  LITHOLOGY. 

Ferruginous  Limestone.  A  compound  of  ferric,  or  hy- 
drated  ferric,  oxides  and  limestone.  The  iron  gives  red 
or  brown  shades  to  the  rock,  dependent  on  the  amount* 
It  is  also  sandy  or  clayey.  It  is  not  peculiar  to  any  forma- 
tion, and  is  found  most  commonly  in  the  "  marbles  "  of  the 
United  States. 

Rotten  Stone.  A  sandy  and  ferruginous  limestone  that 
has  lost  its  lime  from  leaching,  so  that  the  ferruginous  fine 
sand  remains.  It  is  used  for  polishing  purposes.  It  is  a 
porous  rock,  light,  and  found  associated  with  sandy  lime- 
stones. The  loose  calcareous  mica-schists  of  Vermont  are 
sometimes  low  in  lime  and  mica  and  high  in  silica,  and  these 
weather  to  a  coarse  rotten-stone. 

Glauconitic  Limestone.  A  greenish  limestone  with  abun- 
dant grains  of  glauconite.  It  is  found  in  Europe  in  for- 
mations extending  from  the  Trias  to  the  Tertiary,  in  limited 
localities. 

Slaty  Limestone.  This  must  not  be  confused  with  the 
argillaceous  variety,  which  acquires  a  cleavage  from  the 
clay.  In  this  case  the  slaty  cleavage  is  due  to  pressure. 
It  can  only  occur  in  fine  sediments  that  have  been  strongly 
compressed,  and  is  therefore  rare.  It  occurs  at  Solenhofen, 
where  the  fine-grained  rock  cleaves  so  readily  that  it  is  used 
for  slating  purposes.  It  is  sometimes  associated  with  mar- 
ble, and  formed  at  the  same  time,  but  without  the  action 
that  metamorphosed  the  latter. 

Limestones  may  also  be  porous,  nodular,  geodic,  cellular, 
fibrous,  stylolitic,  brecciated,  conglomerated,  and  earthy  ;  as 
well  as  characterized  by  the  fossiliferous  life  from  which 
they  were  formed  by  comminution  of  the  remains,  as  num- 
mulite,  ostaea,  hippurite,  ammonite,  encrinite,  terebratula, 
muschelkalk,  coral-rag,  etc.  In  distinction  from  the  com- 
pact forms  just  noted,  these  last,  characterized  by  the 
varieties  of  animal  life,  are  called  shell  limestones,  coralline 


SECONDARY  ROCKS.  303 

limestones,  encrinal  limestones,  as  they  are  composed  of  the 
remains  of  mollusca,  corals,  or  crinoids. 

(6)  CHALK. 

An  earthy  limestone,  rough  to  the  feel,  friable,  white 
(sometimes  gray  and  light  shades  of  other  colors), 
imparting  its  color  to  whatever  it  is  rubbed  against; 
of  minutely  fine  and  even  grain,  irregular  fracture,  and 
dull  surface. 

This  is  the  result  of  an  extensive  aggregation  of  minute 
animal  organisms  in  the  form  of  oozes  at  the  bottom  of  the 
deep  seas,  so  that  one  million  of  them  are  required  to  form 
a  cubic  inch  of  the  rock  (Ehrenberg).  It  is  usually  pure 
carbonate  of  lime,  but  is  frequently  marly,  and  intermixed 
with  the  shells  of  larger  animals  that  have  dropped  into  it, 
as  well  as  abounding  \\\  flints,  which  will  be  described  later. 
In  some  localities  on  coral  reefs  the  holothurioids  and  other 
animals  that  inhabit  the  reef  form,  by  digesting  the  coralline 
fragments,  a  fine  calcareous  dust  which  solidifies,  to  make 
coral  chalk. 

II.  PHYTOGENIC  LIMESTONES. 
(c]  TRAVERTINE. 

A  somewhat  cellular,  and  concretionary  limestone  formed 
by  calcareous  waters  flowing  over  a  surface,  mainly 
through  the  agency  of  conferva-like  plants. 

This  is  the  method  of  origin  of  a  good  many  travertines ; 
though  there  are  some  due  entirely  to  chemical  action,  as  in 
the  case  of  stalagmite  and  stalactite.  Travertine  is  found 
wherever  waters  highly  charged  with  carbonate  of  lime  flow 
over  the  earth's  surface,  and  sometimes  in  great  masses,  as  at 
Tivoli,  near  Rome,  and  in  this  country  about  the  lakes  of 
the  Great  Basin.  The  hot  springs  of  the  Yellowstone  Park 


3°4  MANUAL   OF  LITHOLOGY. 

have  been  used  as  illustrations  in  all  the  standard  geologies. 
The  travertines  can  be  divided  into  the  shelly  or  loose  sorts, 
which  are  almost  entirely  due  to  life,  and  the  compact  kinds, 
that  are  frequently  of  purely  chemical  origin.  They  are  of 
light  colors  of  red  and  usually  yellow,  and  the  dense  kinds 
have  a  splintery  fracture.  St.  Peter's  at  Rome  is  built  of 
travertine.  Under  this  rock  come  : 

1.  Thinolite  (King).     A  crystalline  travertine  of  unknown 
origin  found  in  the  Mono  and  Lahontan  basins  of  the  western 
United  States.     It  is  pseudomorphed  after  Gay-Lussite. 

2.  Mexican  Onyx.     This  is  a  beautiful  compact  travertine 
in  soft  colors  and  clouded  masses.     H.  3.5  ;   Gr.  2.75.     This 
misnamed  stone  was  first  imported  from  Algiers;  but  the 
exhibit  of  the  Mexican  government  at  Philadelphia  in  1876 
called  attention   to  the  great  extent  of  the  stone  in  that 
country,  so  that  in  the  United  States  it  goes  by  the  name  at 
the  head  of  the  section.     It  occurs  in  bowlders  of  varying 
size  from  a  few  inches  up  to  twelve  feet  in  a  tough  reddish 
or  dark-brown  clay.     In  one  instance  (Antigua  Salines)  it  is 
found  in  a  hard  flintlike  country-rock  that  resembles  "  bastard 
jasper,"  in  "  veins  varying  from  one  inch  to  twelve  inches  in 
width"  (Merrill). 

(d)  TUFA,  Kalktuff. 

A  light,  porous,  cellular,  earthy,  friable  limestone,  formed 
by  plant-life,  and  carrying  an  abundance  of  foreign 
inclusions,  as  leaves,  sticks,  moss,  etc. 

This  is  of  the  same  nature  as  travertine,  but  of  still  more 
porous  structure.  In  the  Great  Basin  of  the  West  it  forms 
large  masses. 

(NOTE.  The  names  "  tuff,"  "  tufa,"  are  variously  used  by 
different  authorities.  They  both  designate  a  light,  porous, 
friable  aggregation,  and  some  authorities  use  one  word  to 
designate  all  such,  using  the  adjectives  "  volcanic "  and 


SECONDARY  ROCKS.  30$ 

"  calcareous  "  to  distinguish  the  two  general  kinds.     In  this 
book  the  "  tuffs  "  are  volcanic,  and  the  "  tufas  "  organic). 

(e)  OOLITE,  Roestone. 

A  limestone  composed  of  minute  concretionary  spherules 
from  the  size  of  millet-seed  to  that  of  a  small  pea,  and 
resembling  the  roe  of  a  fish  (whence  the  name). 

This  rock  was  formerly  thought  to  have  been  formed  by 
concretionary  action  about  grains  of  sand  of  any  sort  in 
waters  charged  with  lime  salts  ;  but  they  are  now  thought  to 
be  the  result  of  algae.  In  the  Great  Salt  Lake  of  Utah  they 
are  now  forming  as  a  scum  along  the  shores,  though  no  traces 
of  lime  are  detected  in  the  waters.  It  has  been  found  that  few 
of  the  waters  of  the  earth's  surface — no  matter  how  high  the 
temperature — are  without  minute  forms  of  life,  and  to  these 
is  due  the  aggregation  of  various  chemical  compounds, — the 
groups  above  named,  for  instance, — and  the  similar  siliceous 
ones  that  will  be  noted  later.  The  grains  of  oolite  are  vary- 
ing in  structure :  compact,  radial-fibrous,  concentric-crys- 
talline, etc.  Oolitic  limestone  is  sometimes  composed 
entirely  of  these  grains,  and  sometimes  they  are  sporadically 
scattered  through  an  otherwise  compact  matrix.  The  lime- 
stones of  Bath,  Portland,  Caen,  etc.,  are  good  examples  of  this 
stone  in  Europe,  and  in  England  the  Upper  Jurassic  is  called 
4t  Oolite."  A  larger  size  of  grain  makes  pisolite,  or  peastone, 
where  the  spherules  are  as  large  as  peas,  or  larger.  These 
are  found  in  hot  springs  carrying  a  large  proportion  of  sol- 
uble salts,  as  at  Carlsbad,  where  the  "  sprudelstein  "  forms. 

2.   DOLOMITE,  Magnesian  Limestone. 

A  granular,  compact,  or  earthy  aggregate  of  dolomite 
(with  more  or  less  calcite) ;  slightly  effervescent  with 
cold  acid.  Gr.  2.87-2.89  ;  H.  3.5. 

Pure  dolomite  or  bitter-spar  carries  54  per  cent  of  car- 


306  MANUAL   OF  LITHOLOGY. 

bonate  of  line,  and  the  rest  carbonate  of  magnesia.  It 
usually  varies  by  having  a  much  greater  proportion  of  lime,, 
and  containing  a  variety  of  ingredients  similar  to  those  in 
limestone.  The  differences  between  the  two  rocks  have 
been  given  under  "  limestone  "  ;  in  addition  it  can  be  stated 
that  calcite  slakes  quickly, to  form  a"  hot"  lime,  while  dol- 
omite slakes  slowly,  to  form  a  "  cold  "  lime.  Many  authori- 
ties hold  that  all  dolomites  are  alterations  in  limestones 
through  infiltrating  solutions  of  magnesia.  This  may  be  the 
case,  as  we  do  not  find  travertine  or  tufa-formations  in  dol- 
omite, but  oolite  is  of  both.  In  the  Silurian  of  Pennsylvania 
alternating  limestones  and  dolomites  are  found  in  the  same 
quarry,  and  Hunt  states  that  dolomite  fossils  are  found  in 
limestones,  while  v.  Richthofen  notes  that  the  dolomites  of 
the  southern  Tyrol  are  from  reef-building  corals.  It  is  prob- 
able that  many  dolomites  are  due  to  the  action  of  magnesia  in 
solution  and  otherwise,  while  an  equally  large  number  were 
formed  directly  from  the  sea  water  by  animal  life,  after  the 
analogy  of  limestone.  They  occur  in  all  of  the  older  geolog- 
ical ages,  and  have  many  names  that  do  not  distinguish  more 
than  the  fossils.  As  a  rock  it  exhibits  granular,  compact, 
earthy,  porous,  cellular,  brecciated,  concretionary,  and  other 
forms.  In  the  last  the  concretions  are  sometimes  as  large  as 
cannon  balls.  It  does  not  exhibit,  or,  at  least,  it  exhibits 
very  rarely,  oolitic,  slaty,  fibrous,  and  stylolitic  states. 

3.  MARL. 

A  compound  of  clay  and  calcite,  or  dolomite  ;  compact, 
earthy,  fissile,  usually  soft ;  crumbles  on  exposure  to 
the  air  ;  effervesces  with  acids  ;  hardness  under  3. 
The  proportion  of  lime  salts  varies  from  20  to  60  per 
cent.     Beyond  these  on  either  side  the  rock  does  not  crum- 
ble on  exposure,  and  is  either  clay  or  one  of  the  limestones. 
It  is  usually  gray,  but  also  yellow,  brown,  greenish,  bluish, 


SECONDARY  ROCKS.  3O/ 

violet,  and  red.  It  may  be  named  after  the  geological  forma- 
tion in  which  it  is  found,  from  the  fossils  it  carries,  from  its 
states  or  its  impurities.  Under  the  next  to  the  last  we  have 
compact,  earthy,  and  shaly  marl ;  under  the  last  calcareous, 
dolomitic,  argillaceous,  sandy,  micaceous,  bituminous,  gyp- 
seous, glauconitic,  shelly,  and  oolitic.  The  copper-slate  of 
Mansfield  is  a  bituminous  marl  carrying  chalcopyrite. 


(B)  SILICEOUS  ORGANIC  AGGREGATES. 

I.  ZOOGENIC  SECTION. 
I.  FLINT,  Feuerstein. 

A  gray  to  black,  compact,  and  intimate  mixture  of  amor- 
phous and  crystalline  silica ;  hardness  of  quartz  ;  frac- 
ture conchoidal  ;  translucent  on  thin  edges ;  occurs 
principally  as  nodules  in  the  upper  chalk  of  Europe, 
where  it  has  been  formed  by  organic  agencies. 

The  first  aggregates  are  the  spiculse  of  glass  sponges, 
echini,  and  brachiopods.  These  on  becoming  triturated 
form  aggregations  into  which  siliceous  solutions  penetrate 
to  consolidate  them  ;  or  form  around  them  by  direct  pre- 
cipitation. 

Chert,  Phthanite,  is  an  impure  flint  which  consists 
sometimes  of  an  aggregate  of  quartz  and  feldspar,  and  some- 
times of  silica  alone.  It  is  found  especially,  though  not 
wholly,  in  limestones,  where  it  has  been  formed  by  similar 
agencies,  as  shown  by  microscopic  sections.  It  is  also  called 
hornstone,  and  much  resembles  felsite,  but  is  distinguished 
by  its  infusibility.  It  is  variously  colored,  and  shows  oolitic 
states.  By  a  considerable  admixture  of  iron  it  passes  into 
jasper,  and,  with  the  addition  of  clay,  to  clay  ironstone.  In 
both  the  above  the  mixture  of  amorphous  and  crystalline 
silica  can  be  detected  by  treatment  with  caustic  potassa. 


308  MANUAL    OF  LITHOLOGY. 

2.  RADIOLARIAN  OOZE. 

A  deep-sea  deposit  formed  on  the  bottom  of  certain  re- 
gions  in  the  western  and  middle  Pacific  Ocean  by 
minute  animals  that  secrete  silica — probably  from  the 
clay  in  suspension  in  those  waters. 

The  deepest  dredgings  (five  miles)  show  that  the  bottom 
of  this  ocean  is  covered  with  the  skeletons  of  these  animals, 
mixed  with  fragments  of  the  spiculas  of  sponges.  Their  size 
is  as  minute  as  in  the  oozes  forming  the  chalk,  already  noted. 

3.  NOVACULITE,  Whetstone. 

A  probable  aggregation  of  calcareous  ooze  where  silica 
has  replaced  the  original  calcite. 

While  some  forms  of  whetstone  are  slaty  from  metamor- 
phic  action,  and  are  highly  siliceous  argillites  or  phyllites, 
the  novaculite  of  Arkansas  is  a  microcrystalline  aggregate 
of  quartz  sand  ;  porous,  and,  according  to  Rutley,  formed 
by  replacement  of  calcite  by  silica,  as  the  structure  (m)  is 
like  flint.  The  Arkansas  variety  is"  snow-white,  with  con- 
choidal  fracture,  and  the  hardness  of  quartz.  The  whet- 
slates  of  Europe  are  either  siliceous  phyllites  of  whitish  to 
greenish  color  (in  some  localities  owing  its  value  to  minute 
crystals  of  manganese  garnet,  of  which  it  carries  a  predom- 
inant portion  of  its  bulk),  or  they  are  siliceous  argillites. 
They  occur  in  Wales,  Devonshire,  the  Thuringian  Forest, 
etc.,  but  in  none  of  these  localities  do  they  resemble  the 
novaculite  of  Arkansas.  A  coarser  oil-stone  is  found  in 
Orange  County,  Ind. 

II.  PHYTOGENIC  SECTION. 

I.  DIATOM-EARTH,  Infusorial  Earth. 

An  aggregate  of  the  skeletons  of  the  microscopic  plants 
called  diatoms ;  whitish,  yellowish,  light-brown. 


SECOND AR  Y  ROCKS.  309 

This  is  forming  now  in  the  south  Pacific  Ocean  at  great 
depths.  It  occurs  in  beds  near  Bilin,  Bohemia,  where 
Ehrenberg  estimated  that  41,000,000,000  of  skeletons  ex- 
isted in  one  cubic  inch.  It  is  also  found  near  Richmond,, 
Va.,  Monterey,  Cal.,  Yellowstone  Park,  etc.  As  varieties 
are  : 

(a)  Tripoli,  Polishing  Slate.     This  is  a  soft  rock  easily 
pulverized,  and  with  slaty  structure,  formed  of  diatom  earth. 
It  is  extensively  used  for  polishing  purposes,  and  is  divided 
in    Bohemia  into  two  varieties — polirschiefer,   soft,  friable, 
not  adhering  to  the  tongue,  and  saugschiefer,  more  solid 
(from  opalizing),  and  adherent  to  the  tongue.    It  is  found  in 
Nevada. 

(b)  Kieselguhr,  Infusorial  Meal,  Diatom  Mud  (Naumann). 
This  is  a  finer  grained  aggregate  than  the  last,  and  is  used 
as  the  "  dope  "  for  dynamite.     It  formed  great  deposits  in 
the  Tertiary  period,  and  is  found  from  Chesapeake  Bay  to 
Richmond,  Va.;   also  in  Nevada,  California,   Oregon,  and 
Utah.    Randanite  is  the  same  rock  from  Algiers  and  France, 
as  named  by  Salvetat. 

2.  FIORITE,  Geyserite,  Siliceous  Sinter. 

An  aggregation  of  opal  silica  through  the  action  of  con- 
ferva-like algse. 

At  one  time  the  formation  of  sinter  was  thought  to  be 
due  to  the  drying  of  the  solution  ;  at  another,  to  its  cooling. 
Through  the  researches  of  W.  H.  Weed  it  is  found  that  the 
aggregation  is  due  to  a  plant  that  grows  an  inch  in  about 
ten  weeks  and  secretes  silica.  The  deposits  are  beautifully 
exhibited  on  a  grand  scale  in  the  Yellowstone  Park.  The 
rock  is  of  two  kinds — sinter,  compact  and  hard  ;  siliceous  tufa, 
less  compact.  It  also  forms  stalactites  on  the  edges  of  the 
basins ;  spheres  and  other  forms  under  the  escaping  waters; 


3IO  MANUAL    OF  LITHOLOGY. 

covers  leaves  and  twig's  with  incrustations,  etc.  The  color 
is  usually  snow-white,  also  yellowish,  grayish,  reddish,  and 
bluish,  according  to  the  impurities  contained.  The  surface 
of  the  deposit  is  wrinkled,  smoothly  irregular,  etc.  The 
mass  is  cheesy  when  first  formed,  but  hardens  on  exposure 
to  the  air.  It  is  found  with  geysers  and  silicated  springs  in 
Iceland,  New  Zealand,  in  great  profusion,  and  as  above 
stated,  in  the  Yellowstone  Park. 

(C)   PHOSPffATIC  ORGANIC  AGGREGATES. 

The  chief  source  of  organic  phosphates  is  zoogenic,  as 
the  amount  of  phosphoric  acid  secreted  in  plants  is  incon- 
siderable, and  its  aggregation  is  under  conditions  that  de- 
stroy all  traces  of  its  origin.  Plants  are  an  ultimate  source 
of  the  element,  as  they  furnish  food  for  animals,  and  thus 
permit  the  concentration  of  phosphorus  in  their  bones  and 
excrements,  shells,  integuments,  etc.  These  during  all  geo- 
logical time  have  been  triturated  and  buried  under  con- 
ditions favoring  the  formation  of  concretions  of  phosphoric 
acid  with  lime  and  clay,  so  that  from  the  beginning  of  animal 
life  on  the  earth  to  the  present  day  there  have  been  aggre- 
gations of  phosphates  as  impregnated  sediments,  as  nodules, 
as  fresh  or  fossilized  remains,  and  as  excrements.  We  can 
distinguish : 

I.  PHOSPHORITE  (Kirwan). 

An  aggregate  of  phosphate  of  lime  ;   compact ;   whitish, 
yellowish,  grayish,  or  brownish. 

Gr.  3-3.2  ;  H.  5  and  less. 

The  "  phosphorite  "  of  Kirwan,  which  included  all  apa- 
tites, has  been  extended  to  include  all  compact  aggregates 
of  phosphoric  acid  of  any  origin.  They  occur  as  uniformly 
disseminated  sediments,  as  nodules  in  various  cements,  and 


SECOND  A  R  Y  ROCKS.  3  I  I 

as  metamorphosed  crystalline   aggregates.      Here  will   be 
treated  "  apatite,"  though  its  origin  may  be  inorganic. 

(a)  Apatite.      A  crystalline,  cleavable,  granular-massive 
aggregate   of   phosphate  of   lime   with   either   chloride   or 
fluoride  of  lime.     H.  (crystal)  5,  (massive)  4.5  ;  Gr.  2.92-3.25. 
Luster  vitreous-subresinous  ;  streak  white  ;  color  sea-green, 
bluish  green,  violet-blue,  sometimes  white,  occasionally  yel- 
low, gray,  red,  brown — usually  dull  colors;    transparent  to 
opaque  ;  brittle.    It  occurs  most  extensively  in  metamorphic 
rocks  of  all  ages,  and  especially  in  metamorphic  limestone. 
It  occurs  massive  in  large  veins  in  limestone  of  the  Lauren- 
tian  near  Ottawa,  Perth,  and   Kingston,  Canada,  where  it  is 
mined  for  fertilizing  purposes.     A  massive,  impure,  altered 
apatite,  earthy,  whitish   to   grayish  color,  and  resembling 
lithographic  stone,  is  called  osteolite,  as  its  composition  is  the 
same  as  that  of  bone.     It  is  found  in  fissures  and  cavities  in 
dolerite,  etc.,  in  Bohemia,  the  Fichtelgebirge,  etc. 

(b)  Phosphate  Rock.     An  aggregate  of  phosphate  of  lime, 
with  calcite,  clay,  and  other  impurities,  occurring  in  beds, 
and   enclosing    fragments   of   shells,   bones,   etc.,   in   small 
amounts.     It  occurs  in  beds  in  the  Bala  limestones  of  Wales, 
in  the  Jurassic  of  Bavaria,  and  elsewhere  in  Europe,  and  in 
the  Devonian  of  Tennessee  under  the  Chattanooga  shale. 
The    last    is    bluish    black,   yellowish,   light-gray,    full    of 
nodules,  shell  impressions,  arid   in  some  cases  resembling 
air-dried  coquina.      It  also  occurs  in   South   Carolina  and 
Florida. 

(c)  Phosphatic  Chalk.     A  series  of  brownish  layers  in  the 
chalk  of  Belgium,  France,  and  England  where  there  is  a 
concentration  of  phosphate,  which  has  replaced  the  shells 
of  foraminifera.     The  proportion  of  phosphate  of  lime  runs 
as  high  as  45  per  cent. 

(d)  Pebble  Phosphate.     This  is  a  concretionary  aggregate 
extensively  developed  from  South  Carolina  to  Florida  as 


312  MANUAL   OF  LITHOLOGY. 

pebbles  of  varying  sizes  imbedded  in  limestone,  clay,  or 
sand.  The  limestone  is  white  and  phosphatic  ;  the  clay  is 
marly,  and  contains,  with  the  nodules,  the  teeth  of  sharks 
and  bones  of  animals,  land  and  marine.  The  concretions 
are  called  by  the  miners  "  hard  rock,"  the  inclosing  lime- 
stone "  soft  rock  ";  "  land  pebble  "  is  the  concretional  deposit 
on  land,  but  when  the  rock  weathers  and  the  concretions 
are  washed  into  the  rivers  with  sand  and  clay,  the  aggrega- 
tion is  called  "  river  pebble."  It  contains  about  26  to  34 
per  cent  of  phosphoric  acid,  and  is  found  near  the  surface 
in  the  river  beds,  and  in  Florida  under  a  thin  covering  in 
the  swamps,  and  is  recovered  by  dredging.  The  land  de- 
posits are  mined  and  treated  by  washing. 

2.  BONE-BRECCIA. 

An  aggregate  of  fragmentary  bones  of  extinct  or  living 
animals,  more  or  less  mixed  with  earth,  sand,  or  lime. 

The  "breccia"  refers  to  the  fragmentary  state  of  the 
bones.  This  is  formed  on  the  floors  of  limestone  caverns, 
either  through  their  having  been  used  as  dens  by  animals, 
or  through  the  accumulation  of  bones  and  other  rubbish 
by  streams  flowing  through  the  caves  or  by  floods.  The 
dropping  waters  from  the  roof  furnished  lime  as  an  ad- 
mixture— in  case  the  cave  was  continually  inhabited — for 
the  accumulations,  or,  in  the  event  of  its  remaining  vacant 
for  long  periods,  covered  the  accumulations  with  a  layer 
of  stalagmite.  In  a  slight  degree  the  cave  earths  formed  by 
the  accumulations  in  caves  through  human  habitation  can 
be  classed  here.  They  will  be  distinguished  by  the  ad- 
mixture of  charcoal,  portions  of  weapons  and  utensils,  and 
other  indications  of  human  residence.  As  caves  are  favorite 
habitations  for  bats,  their  bones  are  found  in  the  loose 
calcareous  tufas  forming  in  caves  of  the  present  period  in 
America. 


SECOND  AR  Y  ROCKS.  3  *  3 

3.  BONE-BEDS. 

Aggregates  of  the  bones  01  land  and  marine  animals  in 
the  older  geological  formations. 

This  is  a  geological  term  for  the  limestone  beds  of  the 
Rhastic  formation  in  Swabia,  Franconia,  Thuringia,  etc.,  and 
in  England  geologists  note  the  "  Lias  bone-bed  "  and  the 
"  Ludlow  bone-bed."  These  beds  are  largely  made  up  of 
the  bones  of  animals.  The  South  Carolina  and  Florida  beds 
are  also  called  "  bone-beds." 

4.  COPROLITE-BEDS. 

Aggregates  of  the  fossilized  excrement  of  vertebrated 
animals. 

These  begin  in  the  Carboniferous  formation,  with  the 
aggregates  of  fossil  excrement  of  ganoids,  with  their  scales 
and  bones.  The  beds  become  more  important  as  we  go 
higher,  and  in  the  Cretaceous  they  are  worked  for  'manure. 
These  beds  are  noted  especially  in  England  and  Europe. 
Logan  reports  a  possible  occurrence  in  the  Lower  Silurian 
of  Canada. 

5.  GUANO. 

An  aggregate  of  the  excrement  of  sea-fowl  formed  on 
islands  in  the  rainless  tracts  off  the  western  shores  of 
South  America  and  Africa. 

This  is  an  earthy,  white,  gray,  or  yellowish  brown  ac- 
cumulation of  unpleasant  odor.  The  absence  of  erosive 
agents  allows  the  accumulation  to  reach  over  100  feet  in 
many  cases,  and  with  it  are  found  inclusions  of  animal  and 
vegetable  life.  The  islands  are  the  roosts  of  sea-fowl,  and 
where  they  form  their  nests. 


MANUAL   OF  LITHOLOGY. 


(D)  CARBONIC  ORGANIC  AGGREGATES. 

These  are  all  vegetable  aggregates,  and  have  generally 
grown  in  place,  but  in  some  cases  have  accumulated 
through  other  influences.  They  can  be  divided  into  rocks 
forming  a  regular  series  from  plant  to  mineral.  All  are  com- 
bustible, black  or  brown,  and  can  be  divided  as  follows  : 

Peat,  or  vegetable  matter  that  has  undergone  little  al- 
teration. 

Lignite,  Brown  Coal,  containing  much  bitumen. 

Coal,  Soft  Coal,  Stone  Coal,  containing  much  less  bi- 
tumen. 

Anthracite,  containing  little  or  no  bitumen. 

Graphite,  without  bitumen,  and  only  combustible  under 
the  blowpipe. 

Semibituminous  coal  and  semianthracite  are  transitions 
between  bituminous  coal  and  anthracite,  and  meta-anthra- 
cite  is  a  transition  between  that  rock  and  graphite. 

In  examining  the  geological  record  we  find  that  the 
recent  formations  are  of  peat,  and  the  oldest  are  of  graphite. 
The  peats  have  undergone  little  consolidating  pressure  — 
the  graphites  have  been  highly  metamorphosed. 

I.  PEAT,  Turf. 

A  yellow,  brown,  or  black  aggregation  of  vegetable  mat- 
ter, varying  from  light  and  fibrous  interwoven  states 
to  compact  and  clayey  ones. 

This  is  a  more  or  less  decomposed  and  chemically  altered 
accumulation  of  vegetation,  dependent  on  its  position  in  the 
mass  and  the  age  of  the  same.  In  old  peat  bogs  that  have 
been  undisturbed  there  is  a  gradual  transition  from  the  light- 
yellowish  or  brownish  yellow  fibrous  aggregate  of  growing 
moss,  through  the  dead  and  brown  fibrous  aggregate  slightly 
below  the  surface  ;  the  still  lower  and  more  compact  mass 


SECOND A R  Y  ROCKS.  3 1 5 

with  brownish  fibers  and  generally  blackish  color ;  the  lower 
black  and  still  more  compact  mass  with  few  shreds  of  fibers, 
to  the  compact  and  creamlike  black  mass  that  may  be  more 
or  less  earthy  or  clayey,  from  admixtures  of  sand  or  clay. 
The  preglacial  beds  are  covered  with  gravels,  and  com- 
pressed into  compact  and  cheesy  masses  that  are  compressi- 
ble with  the  fingers  when  fresh,  but  fracture  with  a  pitchy 
luster  when  suddenly  strained,  and  dry  to  a  hard  mass  with 
.strong  luster.  The  ordinary  peats  resemble,  when  perfectly 
decomposed,  black  clays  when  wet,  and  varieties  of  brown 
coal  when  dry.  Peat  can  be  divided  according  to  the  plants 
from  which  it  was  formed,  as  moss-peat,  heath-,  grass-,  leaf- 
peat,  etc.  The  states  near  the  bottom  of  the  beds  are  called 
mud-peat  and  pitch-peat,  according  to  their  state  of  ag- 
gregation, while  paper-peat  has  been  compressed  strongly 
•enough  to  cleave  readily.  As  accessories  are  found  limonite, 
infusorial  earth,  gypsum,  pyrite,  and  vivianite.  The'weather- 
ing  of  pyrite  forms  an  iron  vitriol,  and  makes  the  variety 
•w/r*0/-peat.  Peat  burns  with  a  strong  pyroligneous  odor, 
and  gives  a  brown  coloration  when  boiled  with  caustic 
potassa,  from  the  presence  of  cellulose.  When  subjected  to 
a  pressure  of  6000  atmospheres,  peat  entirely  loseslts  organic 
structure,  and  forms  a  coal-like  mass  with  brilliant  luster, 
.black  color,  and  great  brittleness. 

II.  LIGNITE,  Brown  Coal. 

A  brown  or  black  earthy  mass,  with  brown  streak,  highly 
inflammable,  compact  or  earthy. 

This  is  a  partially  altered  vegetable  aggregate,  com- 
pressed strongly.  It  shows  traces  of  vegetation  at  times,  such 
.as  stems  with  woody  fiber,  etc.  Its  specific  gravity  varies 
from  0.5  to  1.5,  and  its  carbon  content  from  55  to  75  per  cent. 
As  accessories  are  found  amber,  asphalt,  gypsum,  calcite, 
pyrite,  sphaerosiderite,  and  numerous  organic  compounds. 


MANUAL    OF  LITHOLOGY. 

This  differs  from  "soft"  coal  by  its  greater  content  of 
bitumen,  by  its  pyroligneous  odor  and  its  brown  coloration 
of  boiling  caustic  potassa,  as  well  as  by  its  lower  specific 
gravity  and  hardness.  As  varieties  are: 

(a)  Pitch  Coal.     A  brown  coal  with  pitchy  or  waxy  lus 
ter ;  black,  compact,  and  exhibiting  the  greatest  hardness  of 
all  the  varieties ;  without  traces  of  woody  structure ;  of  the 
highest  density  and  carbon  content  of  the  lignites.    It  occurs 
in  Bavaria. 

(b)  Dysodile,  Leaf  Coal,  Paper  Coal.     Yellowish  brown, 
saddle-colored  laminas  of  the  thinness  of  paper  from  com- 
pression, or  the  presence  of  numerous  leaves  from  which  it 
was  formed.     It  carries  bitumen,  infusorial  earth,  and  clay. 
It  occurs  near  Bonn  and  elsewhere. 

(c)  Moor  Coal  is  a  feltlike  aggregate  resembling  turf. 

(d)  Bituminous    Wood  retains   the  texture  of  the  wood 
from  which  it  was  formed. 

(e)  Pyropissite   (Kengott),    Wax    Coal,   forms   the    upper 
bench  (3$-  feet)  of  certain  brown  coals  in  Saxony.     It  is  a 
dark  grayish  yellowT  to  yellowish  brown  plastic  mass,  with 
greasy,   smirchy   character ;    easily   breaking   with   earthy 
fracture  ;  lustrous  streak ;   Gr.  0.9 ;  lights  in  the  flame  of  a 
candle   and    burns   with   a   clear   flame    (giving    off    much 
steam),  and  forms  a  black  pitchy  mass. 

(/)  Needle  Coal,  from  Alsace  and  elsewhere,  is  an  aggre- 
gate of  acicular  elastic  blackish-brown  particles  with  greasy 
luster  on  fracture.  The  "  needles "  are  often  over  seven 
inches  long. 

(The  Tertiary  lignites  of  Brandon,  Vt.,  have  long  been 
noted  for  their  vegetable  remains  and  especially  the  fossil 
fruits.  Brown  coal  is  found  generally  in  the  Tertiary,  and 
is  a  transition  between  peat  and  coal.) 


SECOND A R  Y  ROCKS.  3 1 7 

III.  COAL,  Soft  Coal,  Stone  Coal,  Pit  Coai,  Bitumi- 
nous Coal. 

A  compact  mass,  usually  brittle,  sometimes  with  distinct 
jointing  or  cubical  cleavage,  sometimes  with  con- 
choidal  fracture ;  colored  shades  of  black ;  streak 
grayish  black  to  brown  ;  burns  less  readily  than  brown 
coal,  but  gives  a  clear  flame  ;  no  pyroligneous  odor, 
but  strong  bituminous  smell ;  usually  friable.  Gr. 
1.2-1.35. 

This  is  distinguished  from  brown  coal  by  its  smell  and 
its  failure  to  afford  a  brown  color  when  boiled  with  caus- 
tic potassa.  It  contains  less  bitumen  than  brown  coal,  but 
shows  in  many  places  aggregates  of  a  charcoal-like  substance 
retaining  the  texture  of  wood,  and  called  by  the  miners 
"  mother  of  coal."  It  contains  from  75  to  90  per  cent  of 
carbon,  and  carries  as  accessories  pyrite  and  marcasite 
{which  are  seldom  absent,  and  give  the  red  and  pink  colors 
to  the  ash),  pyrophyllite  as  linings  of  the  joints,  and  others 
sporadically  distributed.  This  is  found  extensively  devel- 
oped throughout  the  world,  and  especially  in  the  Appala- 
chian coal-field  that  stretches  from  Pennsylvania  to  Alabama 
and  Ohio,  and  in  large  areas,  elsewhere  noted,  in  the  United 
States.  It  has  the  following  varieties : 

(a)  Caking  Coal,  where  the   mass  (whether  solid  or  in 
powder)  fuses  and  runs  together  in  the  fire  to  form  coke. 

(b)  Splint  Coal,  Hard  Coal,  Non-caking  Coal,  breaks  with 
conchoidal  fracture  and  in  large  masses ;  is  not  friable,  nor 
so  easily  inflamed  as  the  caking  coal,  but  leaves  a  loose  ash. 
It  adheres  while  burning,  but  does  not  leave  a  strong  coke, 
nor  does  it  fuse  together. 

(c)  Cherry  Coal,  Soft  Coal,  Sand  Coal,  is  a  softer  coal 
than  the  last,  and  when  powdered  and  inflamed  its  grains 


MANUAL    OF  LITHOLOGY. 

burn  separately  and  do  not  coalesce.     It  has  a  high  resinous 
luster,  is  easily  friable,  and  readily  inflames. 

The  first  two  form  the  gas  coals,  as  they  are  extensively 
used  for  its  production,  and  are  found  abundantly  in  the 
Appalachian  coal-field.  This  form  of  coal  can  still  further 
be  divided,  according  to  texture  or  other  variations,  as  fol- 
lows: 

1.  Cannel  Coal,  Candle  Coal,  Parrot  Coal.    This  is  a  dull 
coal — at  times  appearing  like  black  claystone — that  burns 
witfi  a  clear  flame  like  a  candle.     In  Scotland  it  is  called 
"  parrot,"  from  the  chattering  noise  caused  by  its  cracking 
when  inflamed.      It  breaks  with  a  shaly  to  even  fracture. 
The  more  lustrous  varieties  leave  little  ash,  the  duller  ones 
a  larger  amount.     This  is  found  in  Ohio. 

2.  Torbanite,  Bog-head  Coal,  was  a  formation  (now  ex- 
hausted) in  Scotland  that  carried  a  large  amount  of  ash  and 
of  volatile  matter,  and  was  extensively  used  for  gas-making. 

3.  Jet  is  a  black  variety  of  brown  coal,  compact,  appear- 
ing  like   asphalt,    taking   a   high   polish,    readily    cut    and 
worked,  and   extensively  used  for  jewelry  and  ornament. 
It  occurs  in  small  isolated  masses  in  formations  later  than 
the  Carbonic  in  Franconia,  France,  Yorkshire,  etc. 

IV.  SEMIBITUMINOUS  Coal. 

A  coal  of  general  appearance  like  the  last,  but  differing 
in  chemical  composition  and  density. 

It  varies  from  1.3  to  1.45  in  Gr.,  and  has  but  12  to  20  per 
cent  of  volatile  constituents ;  while  bituminous  coal  has  Gr. 
1.2-1.35,  as  above  given,  and  carries  more  than  20  per  cent 
of  volatile  matter.  Both  of  these  coals  smoke  when  burn- 
ing, especially  at  the  beginning  of  the  inflammation,  and  in? 
this  respect  differ  from  anthracite,  which  burns  without 
smoke  or  smell.  This  coal  is  a  transition  between  the 


SECOND AR  Y  ROCKS.  319 

bituminous  and    semianthracite   coals.       In  Virginia  and 
North  Carolina. 

V.  SEMIANTHRACITE. 

A  coal  with  but  6  to  11  per  cent  of  volatile  matter,  and 
with  Gr.  1.4-1.5  ;  luster  dull,  angular  fracture,  and 
hardness  less  than  anthracite.  In  Pennsylvania,  Ar- 
kansas, etc. 

VI.  ANTHRACITE  (v.  Haidinger). 

An  iron-black  to  velvet-black  coal  with  vitreo-metallic 
luster;  hard  and  brittle;  Gr.  1.5-1.7;  conchoidal  frac- 
ture ;  volatile  matter  under  5  per  cent. 

This  coal  is  "  hard  "  anthracite,  in  distinction  from  the 
semianthracite.  It  burns  with  a  short  flame,  does  not 
easily  inflame,  and  gives  no  smoke.  It  is  found  in  south 
Wales  with  semianthracites  ;  but  the  greatest  development 
is  in  the  Carbonic  of  Pennsylvania,  where  it  covers  large 
areas,  and  is  worked  in  fourteen  named  beds,  and  many 
"  leaders  "  of  varying  thinness.  The  "  anthracites  "  usually 
mentioned  in  other  countries  are  more  of  the  semianthra- 
cite type.  There  is  no  general  distinction  for  this  coal,  as 
it  varies  in  appearance  in  each  bed,  and  in  the  same  bed  in 
different  districts,  and  even  in  the  same  mine.  The  "  Mam- 
moth," "  Baltimore,"  "  Jugular,"  or  other  names  for  the  (E) 
or  largest  bed  of  the  measures,  generally  maintains  an  aver- 
age thickness  of  8  yards,  and  sometimes  reaches  38  yards. 
It  has  a  high  luster,  and  the  middle  "  benches  "  break  with 
a  conchoidal  fracture,  but  the  upper  bench  will  frequently 
exhibit  as  high  a  degree  of  cubical  cleavage  as  in  caking 
coal.  The  (B)  bed,  which  lies  upon  the  Pottsville  conglom- 
erate, sometimes  is  a  bed  8  yards  thick  (Nanticoke),  with 
high  luster  and  no  partings  of  slate ;  twenty  miles  to  the 
north  it  is  a  4-yard  bed  so  entirely  without  luster  that  its 


320  MANUAL    OF  LITHOLOG  Y. 

shipment  with  other  coals  has  condemned  the  mixture  as 
"  slaty."  In  this  respect  it  resembles  cannel  coal  in  having 
a  high  per  cent  of  ash.  The  principal  accessories  are 
pyrite,  marcasite,  and  pyrophyllite,  and  the  presence  or 
absence  of  the  pyrites  grades  the  coals  as  red  or  white  ash, 
the  former  burning  to  a  free  ash,  the  latter  to  a  slaggy 
mass.  The  bottom  clay  of  the  (F)  bed  is  frequently  a 
"  black-band  ironstone." 

VII.  META-anthracite. 

A  metamorphosed  anthracite  occurring  in  regions  of  oro- 
genic  movements;  Gr.  1.8-1.9;  luster  higher  and  hard- 
ness greater  than  in  anthracite. 

This  occurs  in  the  Rhode  Island  (Carbonic)  coal-field  and 
is  found  in  regions  of  greatest  disturbance.  The  coal  has 
become  partially  turned  to  graphite  and  will  only  burn  with 
forced  draught.  All  of  the  Rhode  Island  coal  is  harder  and 
denser  than  that  of  Pennsylvania,  as  it  has  undergone  a  cer- 
tain amount  of  metamorphism. 

VIII.  GRAPHITE,  Black  Lead. 

A  grayish  black  aggregate  of  nearly  pure  carbon ;  flaky 
to  granular  and  compact ;  soft,  with  greasy  feel ;  in- 
flammable under  the  blowpipe  ;  with  metallic  luster ; 
black  streak  (like  lead  pencil).  Gr.  1.9-2.2. 

This  occurs  entirely  in  metamorphic  rocks.  As  acces- 
sories are  silica,  clay,  oxide  of  iron,  hornblende,  mica,  apatite, 
pyrite,  rutile,  corundum,  etc.  It  is  found  in  Siberia,  Bo- 
hemia, Austria,  etc.,  and  in  the  United  States  along  the 
Archaean  area  from  New  York  to  Alabama,  and  in  the  same 
area  in  Massachusetts  and  Michigan.  The  principal  place 
is  near  Ticonderoga,  N.  Y.,  where  it  occurs  in  a  graphite 
schist,  containing  8  to  15  per  cent  of  graphite.  It  is  also 
worked  at  Cranston,  R.  I.,  in  connection  with  the  meta- 


SECOND  AR  Y  ROCKS.  32 1 

anthracite  coal  just  mentioned.  In  the  Rocky  Mountains 
graphite  beds  occur  in  Albany  County,  Wyo.,  Gunnison 
County,  Col.  (where  it  forms  beds  two  feet  thick,  and  very 
impure),  Humboldt  County,  Nev.,  Beaver  County,  Utah, 
and  in  the  Black  Hills  of  South  Dakota.  Graphite  schist 
is  metamorphic,  but  it  is  closely  connected  with  the  fore- 
going, and  as  it  is  sometimes  found  with  phyllites,  it  can  be 
placed  with  them. 

(E)  HYDROCARBONIC  ORGANIC  AGGREGATES. 

I.  ASPHALT,  Mineral  Pitch. 

A  brownish  black  to  black  amorphous  opaque  mass ; 
strongly  smelling  of  petroleum  ;  when  cold,  smooth, 
brittle,  resinous  luster  and  conchoidal  fracture ;  melts 
at  90°  to  100°  C.,  and  burns  with  a  bright  flame,  with 
bituminous  odor  and  much  smoke ;  plastic  at  ordinary 
(summer)  temperatures;  Gr.  1-1.68 ;  streak  paler  than 
the  fractured  surface. 

It  occurs  associated  with  petroleum  as  its  hardened 
form,  as  impregnations  in  rocks  (already  noted  under  lime- 
stones, sandstones,  marls,  etc.),  and  as  independent  beds. 
At  Seyssel,  France,  it  forms  a  large  deposit,  but  the  most 
important  deposit  in  the  world  is  the  asphalt  lake  of  the 
island  of  Trinidad,  ij  miles  in  circumference.  It  also 
exudes  from  the  ground  on  the  borders  of  the  Dead  Sea 
and  in  Sicily.  In  the  United  States  liquid  asphalt  is  found 
in  Ventura  County,  Cal.  An  exceptionally  pure  form  is 
found  near  Fort  Duchesne,  in  the  Uintah  Reservation  of 
Utah,  under  the  name  of  gilsonite  or  uintaite,  which  is  used 
almost  entirely  for  varnish.  Bituminous  sandstones  are 
found  in  California,  Colorado,  Kentucky,  Utah,  and  lime- 
stones in  the  last  State  and  Texas.  The  liquid  bitumen  is 
full  of  vegetable  remains  ;  and  also  carries  varying  propor- 


322  MANUAL   OF  LITHOLOGY. 

tions  of  earthy  contaminations.  It  is  extensively  used  for 
paving  and  forming  the  matrix  for  bricks  formed  of  lime- 
stone breccia. 


II.  OZOKERITE,  Mineral  Wax. 

A  white  (when  pure),  leek-green,  yellow,  brownish  yel- 
low, or  brown  amorphous  mass  ;  translucent ;  greasy  ; 
melts  at  56°  to  100°  C. ;  Gr.  0.85-0.95  ;  ordinarily  it 
is  soft  and  plastic  and  with  fibrous  fracture.  The 
greenish  shades  are  due  to  dichroism. 

Its  name  refers  to  its  waxlike  appearance  and  its  foul 
odor,  but  some  varieties  are  odorless.  It  occurs  principally 
in  Galicia  in  Austria-Hungary,  and  in  the  United  States 
near  Thistle,  Utah.  The  European  product  is  valued  at 
from  $800,000  to  $1,000,000  per  annum.  Occurs  with 
bituminous  clay,  coal,  etc. 

III.  PETROLEUM,  Mineral  Oil,  Kerosene. 

A  thick  to  thin  fluid  ;  colorless,  yellow,  or  brown ;  trans- 
lucent to  transparent.  Gr.  0.7-0.9. 

It  occurs  in  rocks  of  all  ages  from  the  Lower  Silurian  to 
the  present  epoch ;  most  commonly  with  argillaceous  shales 
and  sandstones,  but  sometimes  with  limestones.  It  is  found 
along  the  western  shores  of  the  Caspian  Sea,  in  Italy,  Sicily, 
in  mid-Europe,  at  Rangoon,  Birmah,  and  in  the  United 
States  in  New  York,  Pennsylvania  (especially),  Ohio,  In- 
diana, Virginia,  Kentucky,  Illinois,  Colorado,  and  California. 
Oil,  gas,  and  salt  water  are  found  together  in  the  wells,  and 
when  first  struck  the  oil  is  forced  out  to  great  heights  by 
the  pressure  within,  and  flows  for  varying  lengths  of  time 
till  the  pressure  is  exhausted.  At  the  present  time  the  old 
fields  are  becoming  exhausted. 


S£ CONDA RY  RO CKS.  3 2 3 

IV.    BITUMINOUS    SHALE,    Oil   Shale,    Brand- 
schiefer. 

Shale  containing  sufficient  oil  to  allow  economic  distilla- 
tion ;  pitch-black  to  brownish  black ;  affording  some- 
times a  greasy  streak ;  burning  in  the  fire  with  a 
bluish  flame  when  lit  with  a  match. 

These  shales  are  filled  at  times  with  the  remains  of  fish, 
and  thus  show  the  origin  of  the  oil.  They  probably  repre- 
sent the  shales  from  which  the  petroleum  now  flows,  and 
when  that  shall  have  lost  its  ability  to  flow  the  reservoirs 
will  resemble  the  above  shales.  These  are  extensively  mined 
for  distillation,  though  by  no  means  so  extensively  as  before 
the  discovery  of  petroleum,  but  after  its  exhaustion  their 
value  will  return  again.  They  are  found  in  Scotland,  Ger- 
many, and  in  the  United  States,  as  stated  under  "  Asphalt," 
especially  in  California,  Colorado,  Kentucky,  and  Utah. 

(F)  FERRUGINOUS  ORGANIC  AGGREGATES. 

NOTE. — Microscopic  examination  shows  that  many  lim- 
onites  and  sphaerosiderites  are  aggregated  by  diatoms  and 
confervid  algae,  which  separate  the  iron  from  the  water  to 
form  oolite  or  a  fine  powder.  Some  iron  ores  are,  therefore, 
of  organic  origin,  but,  as  stated  on  p.  295,  all  the  ores  will 
be  treated  as  "  minerals  as  rocks,"  and  found  on  p.  371. 


METAMORPHIC  ROCKS. 

GENERAL    REMARKS. 

Metamorphism  is  a  change  in  rocks  of  so  incomplete  a 
nature  that  there  remain  some  traces  of  the  original  or  in- 
termediate conditions.  Had  the  change  been  complete 
there  would  be  nothing  to  indicate  its  occurrence,  and  we 
would  be  justified  in  calling  the  rock  a  primary  one.  Meta- 
morphism may  be  further  defined  as  a  change  in  form, 
nature,  or  constitution,  or  all  of  them,  through  combinations 
of  heat,  pressure,  or  interstitial  water  (with  the  possible 
presence  of  "  mineralizing  agencies  "  accompanying  intru- 
sives),  and  is  called  local  or  regional,  as  it  is  applied  to  a  large 
or  small  area.  As  far  as  their  results  are  concerned  they 
are  much  the  same  thing  (Barrois).  Local  metamorphism 
occurs  near  and  is  caused  by  the  intrusion  of  a  hot  fluid 
magma.  The  altered  area  is  called  the  aureola.  On  exam- 
ining it  from  its  contact  with  the  intrusive,  where  the  great- 
est metamorphism  has  taken  place,  to  its  edge,  where  it 
gradually  shades  into  the  unaltered  rock,  we  find  no  sudden 
changes  in  alteration  where  lines  of  demarkation  can  be 
drawn  ;  but  rather  a  gradual  shading  of  one  part  into  an- 
other by  differences  that  are  less  perceptible  in  the  broader 
than  the  narrower  aureolae.  These  vary  in  width  from  a 
few  inches  to  four  miles,  and  can  be  usually  divided  into  a 
series  of  bands  or  zones,  which  occupy  quite  proportionate 
widths  of  the  general  belt,  and  which  are  characterized  by 
peculiar  minerals  or  forms  of  alteration.  While  these 
aureolae  are  generally  proportionate  in  width  to  the  bulk  of 

324 


ME TA MORPHIC  ROCKS.  325 

the  intrusive,  they  are  not  wholly  so,  as  metamorphism  has 
been  found  to  be  a  matter  of  heat,  and  the  substances  from 
which  the  new  minerals  have  been  taken  are  generally 
grouped  within  a  small  fraction  of  an  inch  of  the  spot  where 
the  reconstruction  has  taken  place,  so  that  bulk  analyses  of 
unaltered  and  altered  rocks  show  differences  mainly  due  to 
loss  of  water  and  carbonic  acid.  The  heat  of  intrusive 
masses  of  the  same  mixture  may  and  does  vary,  as  shown 
by  variations  in  breadth  of  aureolse ;  and  while  large  masses 
may  show  them  only  on  one  side,  a  small  dike  in  Bretagne 
is  reported  (but  four  inches  wide)  of  well-crystalline  granite 
and  well-defined  aureolas.  Here  the  heat  increment  was 
supplied  by  a  long  flow  through  the  dike-walls.  We  must 
place  duration  of  flow,  therefore,  as  a  principal  agent  in  the 
case,  as  well  as  bulk  of  intrusive,  and  we  must  not  expect  to 
find  the  most  decided  metamorphism  ahvays  about  the 
largest  masses  of  intrusive,  but  it  will  vary  with  the  heat  of 
the  intrusive,  its  bulk,  the  duration  of  its  flow,  the  composi- 
tion of  the  walls,  their  bedding  with  respect  to  the  intrusive, 
and  (from  these  last  two)  the  rate  of  heat-transmission  of  the 
walls.  Other  metamorphic  effects  are  the  bleaching  of 
rocks,  their  coloration,  induration,  and  the  changing  of 
clastic  to  crystalline  texture,  while  the  structure  becomes 
foliated  and  sometimes  parallel-columnar.  These  can  be 
grouped  as  mineralizing  and  caustic.  As  both  are  due  to 
heat,  their  extent  is  a  measure  of  heat,  and  the  great  width 
of  mineralized  aureolae  about  granite  is  as  truly  a  sign  of 
heat — though  there  be  no  fusing  of  dike-walls — as  the  indu- 
ration of  sandstone  for  a  mile  from  a  basalt  dike,  though 
there  be  little  or  no  mineralizing.  We  all  assent  to  the 
eruptive  nature  of  basalt ;  most  authorities  to  that  of  gran- 
ite. The  only  refuge  for  those  who  deny  it  is  to  claim  the 
region  as  a  shear-zone,  where  the  shear  has  furnished  heat 
enough  to  metamorphose  the  country-rocks  and  render  the 


326  MANUAL   OF  LITHOLOGY. 

granite  fluid  ;  but  this  would  destroy  the  dike-walls,  and 
cause  that  shading  of  sedimentary  to  primary  which  is 
never  found  in  nature.  Granite  in  dikes  is,  therefore,  erup- 
tive if  it  shows  a  metamorphic  aureola  and  possessed  a  cer- 
tain amount  of  heat,  but  the  valuation  of  that  amount  is 
differently  reported.  When  it  was  thought  that  mineralizing 
was  due  to  the  introduction  of  new  elements,  it  could  be 
claimed  that  granite  was  cooler  than  basalt  when  erupted, 
but  now  that  heat  does  the  work,  and  as  all  eruptions  carry 
"  mineralizing  "  agencies,  it  becomes  necessary  to  study  the 
effects  of  heat  on  the  vapors  accompanying  eruptions,  and 
the  temperatures  necessary  to  fuse  the  rock  classes.  Barus 
finds  that  basalt  fuses  at  2250°  F.,  while  rhyolite  (granite 
mixture)  is  viscid  still  at  3100°  F.  All  authorities  agree 
that  the  lower  temperatures  of  volcanic  effusion  are  charac- 
terized by  steam,  carbonic  acid,  etc.,  while  the  higher  ones 
have  HC1,  fluoric  and  boric  acids.  Steam  becomes  wetter 
at  low  than  at  high  temperatures.  Dana  well  observes  that 
dry  heat  never  could  indurate  sandstone,  but  the  moisture 
in  the  cooler  flow  of  basalt  would  have  its  dissolving  effect, 
while  the  hotter  and,  perhaps,  somewhat  disassociated  steam 
of  the  hotter  granitic  flow  would  tend  to  desiccate  rather 
than  fuse,  as  wood  has  been  charred  by  impinging  steam. 
It  may  further  be  said  that  granitic  outpourings  were  so  far 
in  the  past  that  the  internal  heat  of  the  earth  had  desiccated 
the  sediments  and  rocks,  so  that  there  was  less  interstitial 
water  than  in  the  more  recent  sediments  and  rocks  through 
which  basalt  extruded,  and  as  moisture  is  a  great  heat-car- 
rier, the  extent  of  induration  is  due  to  this  fact.  It  is  gen- 
erally allowed  that  the  eurites  are  a  granitic  mixture,  and 
the  temperature  of  their  fusion  is  that  of  granite  and  rhyo- 
lite (3100°  F.).  Cole  reports  a  eurite  dike  cutting  an  an- 
desitic  country-rock  (fusing  at  2520°  F.)  and  melting  a  few 
inches  of  the  walls  by  its  greater  heat  (?),  and  sending  into 


ME TAMORPHIC  ROCKS.  Z27 

this  melted  selvage  a  few  of  its  own  intratelluric  pheno- 
crysts  of  pink  feldspar,  so  that  the  cooled  selvage  presents 
the  anomaly  of  a  basaltic  andesite  carrying  phenocrysts  of 
pink  orthoclase.  A  reversed  example  is  where  granite  pyro- 
clasts  are  included  in  eruptive  gabbro,  and  the  granophyre 
fused  to  a  rhyolite  with  flow  structure  and  spherulites. 
Here  the  cooler  (?)  rock  fuses  the  one  solidifying  at  a 
greater  heat.  The  results  of  the  study  of  the  action  of 
included  fragments  seems  to  show  that  the  amount  of  solu- 
tion depends  on  the  dissimilarity  of  the  rocks.  Acid  mag- 
mas have  little  or  no  effect  on  acid  sediments  or  acid  rocks, 
basic  magmas  on  basic  aggregates;  but  basic  magmas  will 
dissolve  acid  rocks,  and  vice  versa.  We  may  conclude, 
therefore,  that  acid  magmas  are  hotter  than  basic,  have  their 
volatile  components  heated  to  the  point  of  association  as 
mineralizers,  form  large  mineralized  aureolas,  and  exhibit 
little  or  no  dissolving  effect  because  the  accompanying  vapor 
is  too  highly  heated  for  fusion,  and  further  because  the 
ordinary  sediments  are  aggregations  of  quartz  mainly,  and 
with  more  acid  than  basic  accessories,  and  therefore  are  not 
readily  acted  upon  by  acid  magmas.  Basic  magmas,  on  the 
contrary,  are  cooler,  have  wetter  steam  and  more  HC1  than 
fluoric  or  boric  acids,  mineralize  slightly,  and  indurate  read- 
ily, both  from  their  acting  upon  more  moist  aggregates,  and 
from  the  acid  character  of  those  aggregates.  Owing  to  the 
greater  exhibition  of  these  effects  along  the  line  of  contact 
of  intrusive  and  country  rock,  local  metamorphism  is  called 
contact  metamorphism,  and  the  same  adjective  is  applied  to 
the  results  of  the  change,  as  contact  rocks,  contact  minerals, 
contact  induration. 

Regional  or  dynamo  metamorphism,  on  the  other  hand,  is 
the  change  produced  over  wide  areas  through  pressure, 
heat,  and  moisture,  irrespective  of  the  presence  or  absence  of 
intrusives.  In  equally  numerous  cases  these  latter  may  have 


328  MANUAL    OF  LITHOLOGY. 

added  their  increment  (locally)  to  the  change,  or  have  been 
involved  in  it.  The  pressure  is  dynamic,  and  not  superin- 
cumbent, and  has  usually  been  the  cause  of  the  heat.  The 
moisture  has  been  usually  interstitial.  As  the  definition  of 
metamorphism  requires  the  retention  of  some  trace  of  ihe 
original  structure,  or  some  evidence  of  a  change,  we  must 
be  able  to  trace  these  rocks  to  their  original  conditions,  or 
find  the  evidences  of  alteration.  The  former  is  possible  in 
many  cases  in  the  field  ;  the  latter  is  possible  sometimes  only 
through  the  microscope.  With  a  ready  escape  for  water, 
and  with  limited  heat  and  pressure,  the  rocks  are  freed  from 
volatile  components,  as  gases  from  soft  coal,  CO2  from  car- 
bonates, moisture  from  sediments,  while  the  particles  of  the 
rock  are  forced  nearer  one  another.  Moisture  allows  crys- 
tallinic  changes,  as  the  rebuilding  of  the  faces  on  clastic 
grains,  so  that  sandstone  becomes  quartzite  and  limestone 
marble.  Metachemism  (Dana)  allows  the  formation  of  new 
minerals  from  aggregates  of  varying  composition  in  the  im- 
mediate neighborhood.  Loss  of  bedding  structure  follows 
and  "  foliation  "  is  induced,  so  that  the  rock  is  no  longer  a 
sediment,  but  a  crystalline  schist.  These  are  the  same  changes 
that  have  taken  place  in  contact  metamorphism,  but  applied 
on  a  grander  scale,  by  lower  heat  and  therefore  during  a 
longer  period.  Following  Dana,  the  changes  may  be 
grouped  as  follows : 

1.  By  small  amounts  of  heat:  discoloration,  drying,  con- 
solidation. 

2.  By  increasing  amounts  :   crystallization  of  sediments. 

3.  By  greater  amounts  :  mineralization. 

These  are  followed  by  incipient  and  (in  regional  meta- 
morphism) complete  fusion,  with  results  that  cannot  be  told 
from  fusion  due  to  other  agencies.  The  resulting  rocks 
depend  on  the  composition  of  the  mass  acted  upon  as  well 
as  its  inclosed  moisture.  Heating  dry  quartz  would  make 


METAMORPHIC  ROCKS. 

no  change,  but  moist  sand  would  become  quartzite.  Alu- 
minous sediments  from  which  the  alkalies  have  been  leached 
form  aluminous  silicates  (cyanite,  garnet,  andalusite),  but 
cannot  form  mica,  which  requires  alkalies,  as  does  feldspar. 
Crystallinic"  metamorphism  has  already  been  noted  as  re- 
building the  faces  of  clastic  grains.  This  is  shown  on  a 
grand  scale  in  the  change  of  clastic  limestone  to  crystalline 
marble. 

Another  series  of  similar  rocks  may  form  on  varying 
scales  through  the  crushing  of  solid  rocks,  as  shown  in  a 
series  of  gneisses  and  other  crystalline  schists  on  the  north 
shore  of  Lake  Superior.  From  all  these  causes  there  arise 
rocks  metamorphosed  from  older  sediments  or  solid  rocks. 
Some  of  them  are  crystalline ;  others  crystalline  and  schist- 
ose ;  others  still  (as  eruptive  gneiss)  have  been  heated  suffi- 
ciently to  become  fluid,  but  not  homogeneous,  and  have 
been  erupted  in  this  state,  as  shown  by  their  aureolae.  All 
are  equally  metamorphic  rocks,  but  there  are  two  grand 
divisions — the  schistose,  and  those  merely  crystalline  and  fused* 
We  can,  therefore,  divide  this  class  into : 

I.  Metamorphic  crystalline  rocks. 
II.  Metamorphic  crystalline  schists. 


I.  METAMORPHIC  CRYSTALLINE  ROCKS. 

• 

These  are  the  results  of  incipient  and  (generally)  of  con- 
tact metamorphism,  and  begin  with  the  caustic  effects  of 
burning  coal-beds  and  of  dikes,  and  extend  through  the 
beginning  of  a  crystalline  texture  in  slates  to  the  complete 
crystallization  of  limestone  through  regional  metamorphism^ 
The  caustic  effects  and  incipient  crystallization  Avill  be  noted 
in  Division  (\a\  and  the  complete  crystallization  in  (I£)  and 
Part  II. 


33O  MANUAL    OF  LITHOLOGY. 

la.   CAUSTIC  EFFECTS. 

PORCELLANITE,  Porcelain  Jasper. 

A  baked  clay,  blue,  gray,  yellow,  brown,  and  red ;  spotted, 
streaked,  clouded  ;  compact,  coarse-schistose,  slaggy  ; 
conchoidal  fracture  ;  translucent  on  thin  edges  ;  dull  or 
slightly  greasy  luster. 

Most  authorities  describe  this  as  the  result  of  the  burning 
of  a  clay-bed  rich  in  feldspar  by  intrusions  of  trap  or  the 
heat  from  burning  coal-beds.  Geikie  seems  to  place  here  the 
hornstone-like  product  of  an  intrusion  in  argillite.  Porcel- 
lanite  is  distinguished  from  both  jasper  and  hornstone  by  its 
ready  fusibility,  and  its  forming  glass  when  heated  with  soda. 

METAMORPHIC  ARGILLITE. 

The  rocks  produced  by  the  variations  in  metamorphism 
are  found  most  closely  associated  in  contact  effects,  as  in 
regional  metamorphism  wide  areas  are  occupied  by  a 
variety  which  may  be  found  occupying  a  zone  of  moderate 
width  about  an  intrusive.  Quite  similar  results  are  found 
about  various  intrusives  along  the  outer  zones,  the  great 
differences  being  [found  along  the  immediate  contact.  This 
is  the  case  in  the  examples  of  metamorphism  in  other  rocks 
that  follow,  and  in  this  and  the  following  descriptions  the 
results  with  a  highly  acid  magma  (granite)  will  be  followed 
by  those  of  a  highly  basic  (diabase)  one.  The  varieties 
found  near  the  contact  are  peculiar  to  contact  metamor- 
phism ;  those  due  to  heat  alone  (moist  heat)  are  found  in 
regional  metamorphisms  also.  Beginning  with  the  outer 
extremity  of  the  aureola,  in  this  and  the  following  cases, 
we  find  in  acid  contacts : 

(a)  Knotty  Slate.  This  has  the  color  of  argillite,  but  in  it 
are  small  darker  knots  or  spots  with  indistinct  margin  which 
are  shown  (m)  to  be  incipient  staurolites  and  andalusites. 
This  shades  into  one  of  the  following : 


METAMORPHIC  ROCKS.  331 

(b)  Staitroltte-s\ate,  where  the  more  micaceous  slate  shows 
•staurolite  ;  ckiastolite-sl&te,  when  it  exhibits  that  mineral ; 
vttrelite  slate,  with  ottrelite  ;  dipyre  slate,  with  phenocrysts  of 
dipyre.     These  shade  into 

(c)  Leptinolite.     Here  the  texture  changes  and  the  rock  is 
like   hornstone.     (m)  it  is  an  aggregate  of  andalusite,  stau- 
rolite, colorless  mica,  and  other  minerals  dependent  on  the 
composition  of  the  intrusive.     With  intrusive  granite  this 
rock  shades  into 

(d)  Cornubianite  (of  Bonney),  when  it  is  a  fine-grained  and 
gneissoid  compound  of  quartz,  mica,  and  tourmaline ;  or 

(e)  Proteolite  (of  Bonney),  when  it  is  a  similar  compound 
of  quartz,  mica,  and  andalusite.     (d]  and  (e)  are  hard,  com- 
pact rocks  and  with  their  ingredients  entirely   (m),  so  that 
they  resemble  (M)  hornstone,  and  fall  under  Geikie's  "por- 
cellanite  "  above.     When  andalusite  is  predominant,  these 
are  called  andalusite  hornstone.     In  none  of  these  last  is  there 
the  perfect  foliation  of  gneiss,  so  that  they  are  better  treated 
here  than  with  that  rock. 

In  basic  contacts  the  outer  zones  are  similar  to  the  above, 
but  the  inner  ones  are  different.  As  they  are  alike  in 
phyllites  and  some  shales,  all  will  be  described  here,  and 
references  made  under  the  other  rocks  to  this  description. 
Instead  of  the  leptinolite,  above  noted,  there  are  two  rocks 
which  vary  in  the  arrangement  of  the  minerals,  as: 

(c')  Spilosite  (Zinken).  Gr.  2.78.  A  fine-grained  to  com- 
pact and  sometimes  schistose,  feldspathic  mass,  greenish, 
with  gray  or  grayish  green  scales  as  large  as  flax-seeds,  and 
weathering  to  a  rusty  brown  color,  scattered  through  it. 
The  similar  state  called 

(dr)  Desmosite  (Zinken)  differs  in  its  density  (Gr.  2.81), 
and  in  the  arrangement  of  the  fresh  or  weathered  spots  in 
distinct  bands  and  layers,  so  that  there  is  an  alternation  of 
white  and  colored  bands.  These  shade  into 


332  MANUAL    OF  LITHOLOGY. 

(ef)  Adinole  (Lessen).  This  differs  from  the  above  in  its 
possessing  a  less  strongly  marked  flat-parallel  structure.  It 
much  resembles  halleflinta,  but  it  is  much  more  fusible.  It 
has  Gr.  2.71  ;  silica  65-80  ;  soda  4-10.  It  is  a  very  compact, 
felsitic,  hornstone-like  rock,  with  conchoid al  fracture,  and  is 
(m)  fine-crystalline.  It  is  colored  green,  red,  and  gray,  and 
with  the  colors  banded  as  in  halleflinta.  All  of  these  are 
varieties  of  "  whet-slates." 

These  states  of  metamorphism  are  found  as  follows: 
Knotty  slate,  chiastolite-,  and  other  slates  in  New  England, 
Scotland,  Wales,  Bretagne,  Pyrenees  ;  spilosite,  desmosite 
and  adinole  in  the  Harz,  and  the  last  also  in  Bretagne  and 
Wales. 

METAMORPHIC   PHYLLITE. 

Taking  a  similar  example  of  a  granite-phyllite  contact,, 
we  will  find  similar  zones  characterized  by  similar  rocks,  the 
difference  being  in  the  greater  proportion  of  mica.  Begin- 
ning with  the  outer  edge,  as  above,  we  find 

(a)  <Fri**/-slate.      This    differs  from    knotty  slate  in  the 
brownish  concretions  resembling  grains  of  corn,  dried  cur- 
rants, etc.  (hence  the  name).     They  have  a  slightly  higher 
luster  and  seem  to  be  made  of  talc  or  mica.     The  slate  itself 
seems  to  have  a  higher  luster,  or  rather  glimmer,  from  the 
creation  of  a  higher  mica  content.     This  shades  into  a  fruit- 
slate  with  more  mica  and  chlorite,  and  this  into 

(b)  Mica-andalusite-s\2ite,  like  a  similar  argillite  reaction, 
but  with  more  mica.     This  shades  into  the  rock  named  above 

(c)  Proteolite  (of  Bonney),  which  is  a  compound  of  quartz, 
mica,  and  andalusite. 

Some  of  the  stages  of  metamorphism  are  represented  by 
other  rocks  called  sericite-phyllite  (Lossen),  which  is  a  (m) 
compact,  greenish,  reddish,  or  violet  sericite-schist ;  and  mica- 
phyllite,  which  is  a  similar  aggregate  of  mica,  compact  and 


METAMORPHIC  ROCKS.  333 

with  silky  luster.  Some  granite-phylhte  contacts  are 
strongly  tourmalinized  to  form  tourmatme-hornstone,  and 
Joiirmatine-schist,  which  is  a  schistose  state  of  the  tourmaline 
rock  noted  under  "  Granite."  The  basic  contacts  with 
phyllite  show  somewhat  similar  states,  and  with  similar 
names  to  cr,  d1 ',  and  er,  under  "  Argillite,"  above.  Adinole  is 
also  a  state  of  metamorphism  in  shales,  and  is  found  as  such 
in  the  Harz  and  the  Taunus. 

METAMORPHIC  SANDSTONE. 
This  is  first  indurated.  The  basic  intrusives  form  green- 
ish colorations  ;  the  granitic  whiten  and  mineralize,  so  that 
with  the  latter  we  find,  as  we  approach  the  contact,  biotite- 
quartzite,  which  shades  into  sillimanite-biotite-qua.rtz\te,  and 
that  to  feldspar-biotite-qu.a.r\.z\ie,  and  these  frequently  contain 
garnet.  Quartzite  and  its  varieties  will  be  fully  described 
later.  Argillaceous  sandstones  form  porcellanite  on  diorite 
contacts.  The  diabase-sandstone  (Trias)  contact  of  Rocky 
Hill,  N.  J.,  shows  tourmaline. 

METAMORPHIC  LIMESTONE. 

The  first  step  is  the  formation  of  marble  ("  marmarosis," 
Geikie).  The  crystalline  product  then  acquires  lime  sili- 
cates in  ordinary  limestone,  and  additional  magnesia  sili- 
cates in  dolomitic  varieties  ;  such  as  garnet,  vesuvianite, 
wollastonite,  and  the  others  noted  under  "  Marble."  At  the 
contact  is  formed  a  calcareous  variety  of  the  hornstone-like 
rock  above  noted,  with  similar  appearance  and  fracture, 
called  time-st/icate-hornstone.  Some  included  pyroclasts 
have  been  altered  to  a  crystalline-granular  aggregate  of  the 
above  minerals  with  abundant  olivine. 

METAMORPHOSED   SCHISTS,  etc. 
These  are  schists  and  primary  rocks  that  have  been  met- 
amorphosed, and  not  metamorphosed  sediments.    Dependent 


334  MANUAL   OF  LITHOLOGY. 

on  the  similarity  or  dissimilarity  of  the  intrusive,  slight  or 
quite  extensive  changes  take  place.  Acid  intrusives  make 
little  change,  beyond  slightly  increasing  the  prominence  of 
certain  minerals  in  acid  rocks;  while  basic  intrusives  in 
basic  rocks  have  still  less  effect.  Intrusives  of  different 
composition  impose  on  the  country-rock  slight  changes,  such 
as  alteration  of  pyroxene  to  hornblende  in  granite-dolerite 
contacts  ;  while  basic-acid  contacts  show  fusing  effects. 

Ib.   METAMORPHIC  CRYSTALLINE  ROCKS. 
CALCAREOUS. 

MARBLE,  Granular  Limestone. 

A  crystalline-granular  aggregate  of  calcite  in  equidimen- 
sional  coarse  to  fine  saccharoidal  grains  intergrown 
together  without  druses  or  pores;  variously  colored, 
and  with  or  without  accessories. 
H.  3  ;  Gr.  2.7-2.8. 

Marble  occurs  in  beds  and  lenticular  masses  between 
metamorphic  schists  and  as  contact  deposits  with  intrusives 
into  limestone.  In  some  cases  the  process  of  metamorphism 
has  softened  the  mass,  so  that  its  beds  become  swollen  and 
appear  like  dikes,  or  are  squeezed  like  apophyses  into  the 
fissures  and  cracks  of  the  inclosing  schist.  The  best  statuary 
marbles  come  from  southern  Europe,  but  very  good  stone 
is  found  at  Rutland,  Vt.  The  trade  name  "  marble  "  differs 
from  the  above  definition  in  including  any  limestone  of  any 
texture  which  is  susceptible  of  a  high  polish  and  desirable 
for  ornamental  purposes.  True  marbles  are  found  in  Canada, 
New  England,  eastern  New  York  and  Pennsylvania,  New 
Jersey,  eastern  Maryland,  Pickens  County,  Ga.,  and  Cali- 
fornia, which  are  mainly  white.  Red  and  reddish  marbles 
are  found  in  east  Tennessee,  Vermont,  Arkansas,  Alabama, 


METAMORPHIC  ROCKS.  335 

Maryland,  Missouri,  New  York,  where  it  has  been  quarried, 
especially  in  the  first  two  states,  and  is  reported  from 
Georgia,  Colorado,  North  Carolina,  and  Wyoming.  Black 
marble  is  found  in  Vermont,  New  York,  Williamsport,  Pa., 
California,  Arkansas,  and  is  reported  as  occurring  in  Colo- 
rado, Illinois,  Tennessee,  and  West  Virginia.  Gray  marbles 
occur  in  New  York,  Virginia,  Tennessee,  and  Arkansas. 
When  the  great  West  has  been  fully  explored,  there  will 
probably  be  deposits  of  this  stone  in  the  metamorphic  areas. 
In  addition  to  the  colors  already  noted  there  are  found  yellow 
and  yellowish  shades,  and  blue  and  bluish  varieties.  The 
purest  white  and  finest  grained  marbles  in  the  world  come 
from  Carrara,  Italy,  and  Paros,  Pentelicon,  and  neighboring 
localities  in  Greece.  As  accessories  in  the  United  States  and 
(J/)  are :  (i)  common  accessories,  muscovite,  serpentine 
(especially  about  New  Haven,  Conn.),  scapolite,  spinel,  talc, 
titanite,  and  wollastonite  ;  (2)  less  common,  in  northeastern 
New  York,  apatite,  corundum,  epidote,  bronzite,  hypersthene, 
rutile,  graphite,  chondrodite,  tourmaline,  actinolite,  vesu- 
vianite,  and  zircon.  At  Muscalonge  Lake  fluorite  crystals 
measuring  one  foot  on  a  side  have  been  found.  These  and 
a  few  others  are  found  in  New  England  and  the  eastern  part 
of  the  Middle  States  along  the  regions  of  uplift.  Freedom 
from,  or  mixtures  with,  these  form  the  following  varieties : 
i.  More  or  less  free  from  accessory  minerals : 
(a)  Statuary  Marble.  A  pure  white  variety,  fine-grained 
and  firm-textured.  The  Parian  marbles  come  from  the  island 
of  Paros,  Pentelican  from  near  Athens,  Carrara  from  Modena, 
Italy,  Luni  from  the  Tuscan  coast.  These  are  the  best  exam- 
ples of  the  variety,  though  here  and  there  in  the  quarries 
about  Rutland,  Vt.,  are  found  quite  good  kinds,  their  chief 
fault  being  too  great  softness. 

(&)  Giallo-antico    is    the    beautiful    Italian   variety    with 
ocher-yellow  to  cream-yellow  color  with  whitish  mottlings. 


MANUAL    OF  LITHOLOGY. 

(c)  Sienna  Marble  is   another  yellow  Italian  kind,  with 
veins  and   mottlings  of  bluish  red  and  (less  frequently)  of 
purple. 

(d)  Red  Marbles.     The  Mandelalo  is  an  Italian  kind,  with 
yellowish  white  spots  on  a  light  red  ground.     Tiree  marble, 
from  Scotland,  exhibits  light  shades  to  rose-red.      Tennessee 
marble   shows  brownish  and  purplish  shades,  and  in  this 
background  the  whitish  fossils  stand  out  prominently.    This 
last  is  only  partially  metamorphic.     The  "  Winooski  "  red 
marble  is  one  of  the  most  handsome  variegated  marbles  of 
the  world.     It   is   found   along   the  eastern  shore  of  Lake 
Champlain,  and  is  harder  than  the  Tennessee  variety. 

(e)  Snowflake  Marble  is  found  at  Pleasantville,  N.  Y.     It 
is  composed  of  snow-white  crystals,  some  of  which  are  over 
an  inch  long.     It  is  reported  as  the  strongest,  most  durable, 
and  purest  in  composition  and  color  of  any  marble  in  the 
United  States. 

(/)  Blue  Marbles.  A  turquois-blue  variety  is  found  at 
Seravezza,  Italy,  a  dark  blue  at  Gouverneur,  N.  Y.,  and  a 
blue  black  at  Glens  Falls  in  the  same  State. 

(g)  Anthraconite  (v.  Moll),  Lucullite,  Nero-antico.  A 
black  marble  found  in  nests  and  veins  in  other  rocks,  and 
(infrequently)  in  beds.  Its  color  is  due  to  carbon,  as  is 
shown  by  its  burning  white.  Black  marbles  are  reported 
(see  above)  in  the  United  States,  but  there  are  no  extensive 
workings.  Anthraconite  in  beds  is  found  near  Christiania. 

2.  With  accessory  minerals  : 

(a)  Cipolino.  An  easily  weathering  white  marble  with 
abundant  pale  greenish  mottlings  and  shadings  from  talc  and 
mica.  These  accessories  become  so  abundant  as  to  impart 
a  distinct  cleavage  to  the  rock,  and  an  increase  in  mica  forms 
a  transition  to  calcareous  mica-schist.  It  is  found  in  Sax- 
ony, Piedmont,  Greece,  and  along  the  Green  Mountains  of 
Vermont. 


METAMORPHIC  ROCKS.  337 

(b)  Ophicalcite  (Brongniart),  Verde  Antique,  is   a   white 
marble  clouded  with  green  from  serpentine.     It  also  exhibits 
yellowish  and  bluish  shades.     The  serpentine  is  in  grains, 
nests,  and  stains,   thoroughly  intermixed   with  the  calcite. 
This  is  interesting  as  being  the  home  of  Eozoon.     It  is  found 
in  Canada  and  New  England  (especially  about  New  Haven, 
Conn.),  and  in  Warren  County,  N.  Y. 

(c)  Calciphyre  (Brongniart)  is  a  marble  porphyritic  from 
phenocrysts  of  garnet,  vesuvianite,  and  augite. 

(d)  Hislopite    (Haughton),    from   Talki,   in  the  East  In- 
dies, is  a  highly  glauconitic  marble. 

(e)  Predazzite  is  a  compound  of  marble  and  brucite,  and 
occurs  at  Predazzo,  Tyrol. 

In  addition  to  the  above,  marbles  may  carry  so  high  an 
amount  of  certain  minerals  as  to  be  styled  tremolitic,  gra- 
phitic, chloritic,  chondroditic,  etc. 

Dolomite  also  forms  a  marble,  but  it  crumbles  from 
weathering,  as  the  calcite  content  dissolves  faster  than  the 
other  and  undermines  the  structure. 


II.    METAMORPHIC   CRYSTALLINE   SCHISTS. 

In  this  division  are  included  rocks  with  but  slight  schist- 
ose structure,  as  they  are  found  associated  geologically  with 
the  schists  rather  than  with  the  contact  formations.  At  times, 
however,  some  of  their  varieties  may  be  found  in  small  zones 
in  contact  aureolae.  Under  the  various  rock  classes  will  be 
found  all  variations  in  metamorphism,  from  the  state  where 
the  original  bedding  and  fossiliferous  content  can  be  dis- 
tinctly traced,  to  the  almost  M^ta-granites,  which  retain  slight 
evidences  of  their  metamorphism,  but  have  lost  all  traces  of 
original  condition.  All  of  these  are  more  or  less  foliated, 
and  shade  from  the  highly  developed  foliation  of  the  general 
body  of  the  group  towards  the  failing  of  foliation  through 


MANUAL   OF  LITHOLOGY. 

its  shading  into  bedding,  on  the  one  hand,  and  through  its 
obliteration  from  almost  perfect  fluidity  of  the  highly  meta- 
morphic  mass,  on  the  other.  We  thus  find  schists  varying 
from  the  incipient  cleavage  of  claystones  through  slates, 
crystalline  and  foliated  phyllites,  to  mica-schist  and  fine- 
grained gneiss.  The  foliation  of  these  rocks  is  usually 
curved  and  crumpled,  but  in  the  less  altered  rocks  it  is  flat- 
parallel,  with  the  layers  unlike  the  laminae  of  strata  in  being 
flat-lenticular  instead  of  flat-plane.  In  cases  of  a  secondary 
metamorphism  imposed  on  schists  there  is  a  secondary  folia- 
tion that  can  be  readily  distinguished.  New  England  is  an 
excellent  field  to  study  metamorphism,  and  especially 
along  the  Green  Mountains,  where  sediments  can  be  traced 
into  schists  within  limited  areas,  and  secondary  foliation  is 
noted  in  Berkshire  County,  Mass. 

The  term  "  schist  "  is  sometimes  loosely  used  to  describe 
coarse  elastics  which  have  been  more  or  less  bent,  but  which 
have  not  become  crystalline-granular.  It  is  not  so  used  in 
these  pages,  but  refers  only  to  those  crystalline-granular 
rocks  which  are  foliated.  All  crystalline  rocks  without  foli- 
ation are  "  rocks.''  This  has  already  been  stated,  but  it  is 
repeated  here,  as  the  following  pages  will  contain  descrip- 
tions of  crystalline  rocks  (so  called)  which  are  found  with 
schists,  but  are  unfoliated,  or  but  slightly  crumpled.  It  re- 
mains to  say  that  cleavage  is  not  taken  as  foliation.  Both 
may  be  due  to  the  same  or  similar  causes,  but  the  argillites 
and  phyllites  will  be  classed  with  the  "  rocks,"  and  the  mica- 
schists,  into  which  they  shade  by  regular  gradations,  will 
fall  into  "  schists/'  In  German  the  same  word  (sckiefer}  is 
used  for  schists,  slates,  and  shales,  though  they  are  separated 
in  classifying  rocks,  and  occasion  some  trouble  to  the  begin- 
ner who  consults  books  in  that  language. 

Summing  what  has  been  said  of  the  origin  of  schists  and 
adding  thereto,  we  find  that  they  may  come  :  from  the  origi- 
nal crust  (?)  of  the  molten  globe  ;  as  true  eruptives  in  the 


METAMORPHIC  ROCKS.  339 

early  geological  ages  ;  as  tuff  states  (?)  of  old  eruptives  :  or 
as  sediments  altered  by  deep  burial,  metachemism,  or  oro- 
genic  action.  The  results  will  be  so  similar  that  no  division 
can  be  made  from  hand  specimens,  and  the  eruptive  origin 
can  only  be  seen  in  the  contact  aureola  of  the  rock.  We  can 
divide  them  roughly  according  to  the  mineral  components,  as 
in  the  eruptive  rocks,  but  less  closely,  as  there  is  a  broader  mix- 
ture of  minerals,  owing  to  the  varieties  of  origin  and  amounts 
of  metamorphism.  Those  having  predominant  quartz  and 
with  silica  over  55  per  cent  will  be  classed  as  acid,  while 
those  with  a  lower  silica  content  will  be  grouped  as  basic. 

ACID  SERIES. 

The  rocks  of  this  series  are  more  or  less  foliated,  crystal- 
line-granular, generally  (M)  compounds  of  quartz, 
feldspar,  mica,  with  various  accessories ;  coarse  and 
fine-grained  and  (M)  compact ;  massive  or  fissile ; 
variously  colored. 

Silica  55-82;  Gr.  2.6-3.2. 

They  can  be  divided,  according  to  the  predominant  minerals,  as  follows. 
QUARTZ  GROUP  : 

Quartzite,  quartz-schist,  itacolumite,  Lydian  stone. 
QUARTZ-MICA  GROUP. 

Mica-schist  and  its  varieties. 
QUARTZ-TOURMALINE  GROUP. 

Tourmaline-schist,  tourmaline-hornstone. 
QUARTZ-IRON  GROUP: 

Itabarite,  micaceous  iron-schist. 
QUARTZ-FELDSPAR  GROUP: 

Granulite,  gneiss  and  its  varieties. 
QUARTZ-FELDSPAR-MICA  GROUP: 

Halleflinta,  porphyroid,  (adinole). 
FELDSPAR-MICA  GROUP  : 

(Cornubianite). 

Adinole  and  cornubianite  have  already  been  described,  and  are  in- 
cluded in  the  above  to  show  where  they  would  come  in  the  series  if  their 
connection  with  contact  products  did  not  place  them  in  a  previous  series. 


34°  MANUAL  OF  LITHOLOG  Y. 

QUARTZ   GROUP. 

QUARTZITE. 

A  granular  to  compact  aggregate  of  quartz  with  coarse- 
splintery,  conchoidal,  and  vitreous  fracture,  and  with 
few  or  no  signs  of  foliation. 

This  occurs  in  beds  with  crystalline  schists,  and  in  some 
cases  hundreds  of  feet  thick.  It  also  occurs  in  regions  of 
sediments  where  crystallinic  metamorphism  has  filled  the 
interstices  of  a  sandstone  to  form  a  compact  rock.  Both 
kinds  are  generally  associated  with  the  oldest  formations. 
Quartzite  is  found  along  the  Appalachian  region  of  the 
eastern  United  States.  It  is  generally  white,  sometimes 
yellowish  white,  yellow,  red,  and  blue.  The  grains  can 
generally  be  distinguished  (M) ;  but  sometimes  the  rock  is 
so  fine  that  they  can  only  be  seen  (m),  and  it  resembles  the 
Arkansas  novaculite  when  white,  and  some  flints  when 
colored.  It  is  a  true  sediment,  and  retains  its  bedding  and 
other  characteristics.  The  quartzite  of  South  Bethlehem, 
Pa.,  has  almost  lost  its  original  habit,  and  breaks  with  a 
conchoidal  fracture,  while  its  lower  portion  is  porphyritic 
with  feldspar  phenocrysts.  The  same  rock  twenty  miles  to 
the  southwest,  at  Fleetwood,  Lyons,  etc.,  is  the  crumbly 
Potsdam  sandstone  with  unchanged  bedding  planes  and 
riddled  with  casts  of  scolithus.  The  South  Bethlehem  rock 
is  light  or  dark  gray  ;  the  Fleetwood  rock  white,  yellowish, 
or  reddish.  Quartzite  also  occurs  as  a  contact  formation 
with  intrusive  dikes,  and  forms  a  zone  of  a  few  feet  in  thick- 
ness. In  still  further  cases  the  rock  seems  to  be  solid  (M) 
quartz,  of  great  purity  and  high  translucence — almost  be- 
coming subtransparent,  and  exhibits  a  highly  developed 
flat-parallel  cleavage.  It  frequently  shows  well-developed 
cubical  jointing.  As  accessories  occur  (abundantly)  chlorite, 
magnetite,  pyrite,  and  specular  hematite.  The  last  occurs 


METAMORPHIC  ROCKS.  34 * 

in  hand  specimens  in  Virginia  in  thin  plates  parallel  to  the 
cleavage  of  the  quartzite.  Other  accessories  are  carbon,, 
graphite,  rutile,  apatite,  tourmaline,  garnet,  cyanite,  mica,, 
ottrelite,  etc.  The  last  occurs  in  a  fine  blue  quartzite  near 
Rutland,  Vt,  the  color  showing  strongly  when  the  rock  is 
wet,  and  fading  when  dry.  As  varieties  are : 

(a)  Oolitic  Quartzite.      In  concretions  weighing  several 
hundredweight  in  the  "  sandy  barrens  "  of  Center  County, 
Pa.,  in  the  limonite  mines.    The  same  form  is  reported  from 
Sumatra.     The  variety  shows  spheroidal  grains  one-twelfth 
of  an  inch  in  diameter.    The  Center  County  variety  may  be 
a  replacement  of   calcite   by  silica,  as  the  "  barrens "  are 
formed   by  the   leaching   of   the  former  mineral  from  the 
calciferous  sand-rock. 

(b)  Buhrstone  (Hitchcock)  is  a  similar  rock  as  far  as  origin 
is  concerned,  and  forms  a  compact  quartzite  with  irregular 
pores  that  occurs  in  Berkshire  County,  Mass.,  and  along  the 
Appalachian  border  from  South  Carolina  to  Georgia.     The 
rock   is   more    mineralogical   than   economic,  as   it   is   not 
worked,  the  best  millstones  of  the  United  States  being  from 
the  Berea  (O.)  grit.    The  best  buhrstones  come  from  France. 

These  two  varieties  have  been  described  under  organic 
aggregates  of  silica,  but  are  again  noted,  as  their  organic 
origin  is  only  probable.  The  various  accessories  named 
above  are  frequently  predominant  enough  to  form  varieties 
bearing  their  names,  as  tourmatme-quartzite,  etc. 

QUARTZ-SCHIST. 

A  foliated  quartzite,  usually  with  some  mica. 

This  may  be  taken  as  a  mica-schist  with  the  silica  in  ex- 
cess  of  82  per  cent,  but  with  sufficient  mica  to  impart  a 
schistose  structure.  A  failure  of  the  mica  places  the  rock 
in  "  quartzite,"  and  an  increase  of  the  mineral  in  "  mica- 
schist."  Geikie  notes  large  tracts  in  the  Scottish  Highlands 


342  MANUAL    OF  LITHOLOGY. 

where  the  rock  is  a  transition  between  quartzite  and  mica- 
schist,  and  varies  from  one  extreme  to  the  other  —  the  mica 
allowing  the  rock  to  be  split  into  flagstones.  In  the  Green 
Mountains  of  Vermont  quartz-schist  occurs,  and  with  a 
further  change  (by  the  entrance  of  calcite)  into  calciferous 
quartzite  and  calciferous  mica-schist.  In  the  same  region 
also  occurs  : 

Conglomerate  Schist.  This  is  a  transition  between  a 
quartz  conglomerate  and  a  gneiss.  The  pebbles  of  the  con- 
glomerate are  sometimes  only  slightly  flattened,  and  may 
reach  several  inches  in  diameter.  They  are  then  inclosed 
in  a  schistose  matrix,  so  that  they  can  be  readily  distin- 
guished from  an  unaltered  conglomerate.  In  other  cases 
the  rock  has  been  so  strongly  compressed  that  the  pebbles 
are  flattened  to  long  lenticules  with  rounded  ends,  and  still 
further  metamorphism  changes  them  to  lenticular  folia  of 
crystalline  quartz,  with  no  traces  of  their  original  shape. 
This  is  reported  from  the  Alps,  Saxony,  Norway,  France, 
Ireland,  Scotland,  and  the  Green  Mountains. 

ITACOLUMITE    (v.   Eschwege),     Flexible    Sand- 
stone. 


A  fine-grained  and  schistose  aggregate  of  quartz, 

dered   flexible,  when  in    moderately  thin  plates,  by 
parallel  laminae  of  mica,  talc,  chlorite,  and  sericite. 

This  was  first  described  at  the  mountain  Itacolumi  in 
Brazil,  where  the  formation  is  of  great  thickness  and  extends 
several  miles  —  the  mountain  being  5400  feet  high.  It  also 
occurs  in  the  Southern  Atlantic  States  of  the  Union  and  in 
Pennsylvania.  Some  authorities  class  this  as  a  sandstone. 
As  accessories  are  micaceous  hematite,  magnetite,  martite, 
native  gold,  and  diamond. 


METAMORPHIC  ROCKS.  343 

LYDIAN     STONE,     Siliceous     Schist,     Phthanite 
(Haiiy),  Touchstone. 

A  cryptocrystalline  aggregate  of  quartz,  with  clay,  car- 
bon, and  oxide  of  iron  ;  black  or  dark-colored  ;  hard  ; 
infusible ;  with  splintery  fracture. 

This  occurs  in  thin  bands  in,  and  later  than,  the  Silurian, 
and  appears  to  be  an  original  and  not  a  metamorphic  rock, 
as  the  beds  with  which  it  is  intercalated  are  not  altered.  It 
also  abounds  in  fossils  (graptolites,  for  example) ;  but  its 
general  appearance  is  that  of  a  schistose  rock.  It  can  be 
placed  here  or  with  sandstone  with  equal  propriety.  It  is 
reported  from  the  Carbonic  of  the  Appalachian  area.  It 
was  formerly  used  in  distinguishing  native  metals  and  their 
alloys  by  their  streaks  on  the  fine  dark  surface. 

QUARTZ-MICA   GROUP. 

MICA-SCHIST,  Mica-slate. 

A  schistose  aggregate  of  quartz  and  mica  in  widely  vary- 
ing proportions. 

Silica  55-82;  Gr.  2.7-3.17. 

It  occurs  in  extensive  formations  in  the  metamorphic 
areas  of  the  world,  and  as  inner  contact  zones  of  great  width 
about  bosses  of  granite,  and  is  found  in  the  Archaean  forma- 
tions throughout  the  world.  It  is  always  crystalline  and 
foliated,  but  varies  in  almost  every  other  character,  as  the 
mica  varies  from  the  condition  of  an  accessory  to  that  of 
being  almost  the  sole  ingredient.  The  texture  sometimes 
becomes  so  slightly  foliated  that  the  rock  becomes  almost 
wholly  granular-massive.  The  two  ingredients  frequently 
are  not  equally  mixed,  but  aggregate,  in  folia  of  varying 
thickness,  to  form  a  flat-parallel  structure.  At  times  the 
mica  is  in  knots  of  varying  size  which  are  connected  in  the 
quartz  matrix  by  strings  of  mica.  In  other  varieties  the 


344  MANUAL    OF  LITHOLOGY. 

quartz  forms  large  plates,  strings,  or  segregations  about 
which  the  mica  is  grouped.  There  are  few  rocks  in  which 
so  great  a  variety  of  arrangement  of  ingredients  and  of 
structures  exist.  The  mica  is  usually  muscovite  or  biotite— 
more  generally  the  former,  which  is  of  white  color.  The 
greasy  varieties  (formerly  thought  to  be  talc)  were  found 
by  Dewey  to  be  damourite,  and  varieties  carrying  them 
were  named  by  Dana  /*jj>dfo?mica-schists.  It  happens  fre- 
quently that  both  biotite  and  muscovite  are  together,  to 
make  a  mottled  rock.  The  quartz  is  in  grains  or  larger 
aggregates,  as  already  noted.  As  accessories  occur  abun- 
dantly calcite,  feldspar,  garnet,  tourmaline,  hornblende, 
andalusite,  iolite,  staurolite,  chlorite,  rutile,  graphite,  iron 
ores,  talc,  and  cyanite,  so  that  varieties  are  formed  through 
them.  In  the  contact  zones  about  granite  occur  also  silli- 
manite,  fibrolite,  and  epidote.  The  various  textures  and 
structures  form  another  class  of  varieties,  so  that  from  the 
above  many  are  noted  by  various  authorities.  Especially 
prominent  are : 

(a)  Damourtte-schist,  //^fo?mica-schist  (Dana).  This  is 
a  soft  rock  with  damourite  or  one  of  the  hydromicas  re- 
placing mica.  It  occurs  as  alterations  of  older  rocks,  such 
as  crushed  diorites,  and  as  beds  in  slightly  metamorphic 
sediments.  In  eastern  Pennsylvania  there  are  two  damour- 
ite beds,  the  lower  being  between  the  Potsdam  sandstone 
and  the  gneiss,  and  the  other  between  the  Hudson  slates  and 
the  Silurian  limestone.  This  forms  the  matrix  of  the  sub- 
glacial  till  along  the  northern  border  of  the  South  Moun- 
tain, at  Bethlehem,  Pa.  It  also  is  found  along  the  Taconic 
region,  in  Canada,  and  along  the  Laurentian  of  the  Atlantic 
States.  It  is  usually  in  light  colors,  that  just  noted  being 
shades  of  cream.  The  compact  state  is  called  agalmatolite. 
It  occurs  in  the  Alps  as  paragonite-sc\\\st,  when  this  form  of 
mica  is  predominant. 


METAMORPHIC  ROCKS.  345 

(b)  Calcareous  Mica-schist.  A  fissile,  crystalline-granular 
aggregate  of  quartz,  mica,  and  calcite,  of  all  degrees  of 
coarseness,  and  all  extents  of  variation  in  the  proportions  of 
the  components.  The  variety  from  the  Erzgebirge  is  a 
foliated  limestone,  and  a  transition  between  cipolmo  and 
mica-schist.  In  the  eastern  Alps  the  rock  consists  of  alter- 
nate layers  of  mica-schist  and  limestone.  The  varieties  of 
central  Vermont  are  a  most  intimate  mixture  of  the  ingre- 
dients in  variable  proportions.  At  times  there  is  a  fine- 
granular  and  slightly  foliated  mixture  in  which  quartz  is 
predominant,  so  that  it  resembles  a  slightly  micaceous  cal- 
ciferous  sand-rock  on  a  fresh  fracture,  but  the  weathered 
specimens  show  the  difference  in  composition  to  a  high 
degree,  as  they  lose  their  calcite  and  leave  the  quartz  deeply 
rusted  from  the  decomposed  mica,  so  that  the  weathered 
stone  can  be  readily  crumbled  with  the  fingers,  and  forms 
"  rotten  stone."  Other  varieties  in  the  same  region  consist 
almost  entirely  of  mica  (predominant),  and  large  knots  or 
concretions  of  cream-colored  calcite  or  dolomite,  drawn  out 
to  form  "  eyes  "  in  the  dark  mass.  A  third  variety  shows 
predominant  quartz  with  calcite  and  subordinate  mica.  The 
calcite  exhibits  cleavage  surfaces  on  a  fracture,  some  of  which 
are  £  inch  across.  The  variety  at  Woodstock,  Vt.,  abounds 
in  garnet  ofAll  sizes  up  to  that  of  the  fist.  Other  accessories 
are  tourmaline,  hornblende,  epidote,  magnetite,  graphite,  and 
talc — the  last  sometimes  replacing  mica  to  form  calcareous 
taic-schist. 

The  following  varieties  are  also  worthy  of  note:  chlorit- 
oid,  from  the  Alps ;  tourmalinic,  from  Saxony,  the  Green 
Mountains,  etc.  ;  double  mica,  nacritide  (Schill),  with  both 
micas,  from  Saxony,  Pike's  Peak,  Kansas ;  gneissic,  from  the 
Erzgebirge;  garnetiferous,  a  common  variety;  graphitic, 
from  Saxony,  the  Pyrenees,  Norway,  etc. ;  andalusitic,  from 
Sweden,  Spain,  Ireland,  Tyrol,  etc.  Many  of  these  are 


34-6  MANUAL    OF  LIT  HO  LOG  Y. 

found  in  New  England.  Hornblendic  mica-schist  will  be 
noted  later  under  "  Hornblende-schist."  An  epidote-glauco- 
is  reported  from  the  island  of  Celebes. 


QUARTZ-TOURMALINE    GROUP. 

TOURMALINE-SCHIST. 

A  foliated  granular  aggregate  of  quartz  and  tourma- 
line. 

This  is  not  the  schistoid  state  of  the  compound  of  quartz 
and  tourmaline  noted  under  "  Granite,"  but  a  contact  product 
of  granite.  In  this  rock  the  tourmaline  is  in  granules  and 
acicular  crystals,  and  the  rock  as  a  whole  is  fine-granular 
and  black.  While  tourmaline-quartzite  and  tourmaline  rock 
are  formed  from  the  granite  by  the  influence  of  the  boric 
and  fluoric  acids,  this  and  the  next  rock  are  formed  by  simi- 
lar agents  from  the  country-rock.  Tourmaline-schist  occurs, 
therefore,  as  an  inner  contact  zone  of  an  intrusive  granite 
with  phyllite  and  similar  rocks,  and  is  found  in  Cornwall,  in 
the  Erzgebirge,  and  elsewhere. 

TOURMALINE-hornstone. 

A  (M)  compact  aggregate  of  quartz  and  tourmaline  with 
mica,  staurolite,  iron  ores,  etc.  ;  with  splintery  frac- 
ture ;  slight  foliation  ;  grayish  color. 

This  is  the  tourmaline  representative  of  the  ordinary 
hornstone  formed  in  granite  contacts  without  exhalations  of 
the  above-noted  mineralizing  acids,  and  the  similar  lime- 
siiicate-hornstone  of  the  contacts  with  limestone.  (M)  it 
cannot  be  told  from  the  above  when  compact,  and  it  is  only 
by  following  it  into  parts  of  the  aureola  where  tourmaline 
appears  (M)  that  the  variety  can  be  known.  It  is  readily 
told  when  examined  (m).  It  is  found  in  Cornwall,  Saxony, 
Bretagne,  Norway,  and  at  Mount  Willard,  N.  H. 


METAMORPHIC  ROCKS.  347 

With  this  formation  of  tourmaline  there  is  also  a  growth 
of  topaz,  so  .that  in  the  breccias  of  tourmaline-quartz-schist 
there  occur  nests  and  veins  of  topaz  (crystal,  granular,  com- 
pact), as  on  the  granite-phyllite  contact  of  the  Schnecken- 
stein  in  the  Voigtland,  to  form  "  topasbrockenfels." 

QUARTZ-IRON   GROUP. 

ITABIRITE  (v.  Eschwege). 

A  granular  to  compact  aggregate  of  quartz,  micaceous 
hematite,  and  magnetite. 

It  appears  to  be  a  highly  ferruginous  mica-schist,  and 
"with  itacolumite  forms  Mount  Itabtra  in  Brazil.  It  is  also 
found  in  the  Carolinas,  at  Sutton,  Canada,  Norway,  and  on 
the  Gold  Coast  of  Africa.  It  is  black  and  violet  in  color, 
and  has  the  iron  ores  as  predominant  minerals,  with  quartz 
sometimes  quite  an  unimportant  ingredient,  while  at  other 
localities  the  quartz  forms  white  lenticular  strings,  so  that 
the  mass  has  a  decided  schistose  appearance.  As  accessories 
occur  talc,  chlorite,  hornblende,  biotite,  garnet,  gold,  epidote, 
.and  feldspar.  On  weathering  it  forms  a  sand  called  jacottnga. 

MICACEOUS  IRON-SCHIST. 

A  granular  schistose  aggregate  of  quartz  and  micaceous 
iron. 

It  occurs  in  beds  in  metamorphic  regions,  and  is  found 
In  Brazil,  Hungary,  South  Carolina,  etc.  The  quartz  is  in 
white  grains  (usually  grayish  white),  scattered  between  the 
folia  of  micaceous  hematite.  These  latter  are  black,  and  so 
evenly  arranged  that  the  rock  seems  dotted  with  white  in 
.stripes.  In  the  iron  region  of  Virginia,  near  Lynchburg,  a 
similar  rock  appears  with  the  two  minerals  in  masses,  the 
quartz  being  predominant  and  the  hematite  forming  plates 
an  inch  broad,  so  as  to  impart  a  somewhat  flat-parallel  struc- 
ture to  the  rock. 


34^  MANUAL   OF  LITHOLOGY. 

QUARTZ-FELDSPAR  GROUP. 

GRANULITE  (Weiss),  Leptynite  (Haiiy). 

A  slightly  foliated  fine-grained  aggregate  of  granular 
quartz  and  feldspar,  usually  with  small  garnets. 
Silica  70-80 ;  Gr.  2.6-2.7. 

This  is  a  gneiss  without  mica,  and  occurs  locally  in  Ar- 
chaean formations.  It  is  especially  developed  in  the  eastern 
part  of  North  America.  In  Canada  it  is  known  locally, 
north  of  Lake  Ontario  as  "  huckleberry  rock."  The  Second 
Geological  Survey  Reports  of  Pennsylvania  place  here  the 
non-garnetiferous  mass  of  the  South  Mountain  at  its  eastern 
extension  between  the  Delaware  and  Schuylkill  rivers.  At 
times  the  foliation  is  so  indistinct  that  it  might  be  called 
aplite,  were  it  not  for  the  presence  of  garnet.  The  quartz  is 
white,  and  occurs  in  grains  and  strings,  which  give  a 
schistose  appearance  to  the  mass.  The  feldspar  is  usually 
orthoclase  (microcline,  microperthite)  of  pale  reddish,  yel- 
lowish, or  white  color;  or  plagioclase  (oligoclase)  in  rare 
cases.  Garnet  is  red,  and  from  (m)  proportions  to  the  size 
of  peas,  rounded  or  roughly  crystal,  sometimes  flattened  like 
the  quartz  till  as  thin  as  a  sheet  of  paper,  and  forming  red- 
dish specks  on  a  fracture  parallel  to  the  foliation.  Among 
the  accessories  is  biotite,  which  makes  transitions  to  gneiss, 
so  -that  we  can  have  the  two  intermediate  rocks  biotite- 
granulite  and  ^wm-granulite.  The  following  accessories 
are  frequently  so  abundant  as  to  form  rocks  with  similar 
names,  as  ^/^^/V^-granulite,  garnet-granulite,  tourmatine-gran- 
ulite.  The  variety  in  eastern  Pennsylvania  can  be  called 
^07-^/^/z^-granulite,  as  it  varies  between  that  rock  and  horn- 
blende-gneiss. Pyroxene-grauulite,  /lyfierstkene-granulite,  and 
^^//dg^-granulite  are  basic  forms  occurring  in  Saxony.  If 
mica  occurs,  it  is  usually  dark  brown  to  black  (Zirkel) ; 
"usually  a  white  variety  of  mica,  seldom  black"  (v.  Cotta). 


METAMORPHIC  ROCKS.  349 

The  ordinary  granulite  is  white,  yellowish,  or  flesh-red,  with 
garnet  and  cyanite  (Rosswrein,  Saxony);  striped  granulite 
has  the  components  in  parallel  stripes  (on  the  Zschopau, 
Saxony) ;  black  granulite,  from  iron  (Penig,  Saxony).  The 
rock  is  characterized  by  regular  jointing  parallel  to  the 
foliation,  and  an  irregular  cross-jointing  with  smooth  part- 
ings. The  Pennsylvania  rock  shows  abundant  slickensides 
as  large  as  the  palm  of  the  hand. 

QUARTZ-FELDSPAR-MICA   GROUP. 

GNEISS  (old  miner's  term  for  the  rock  containing 
the  ore). 

A  schistose  granular  aggregate  of  quartz  and  feldspar 
(potash,  soda,  or  lime-soda)  with  one  of  the  black  bi- 
silicates,  preferably  the  micas.     A  foliated  granite. 
Silica  56-75  ;  Gr  2.6-2.8. 

It  occurs  in  widespread  masses  in  the  Archaean  forma- 
tions of  the  earth,  especially  in  Scandinavia,  Scotland,  and 
the  eastern  part  of  North  America,  where  it  forms  a  V-shaped 
area  extending  from  Labrador  to  New  York,  and  thence  by 
the  north  shore  of  Lake  Superior  to  the  Arctic  Ocean,  with 
a  narrow  tongue  southward  from  New  York  to  Alabama 
along  the  Atlantic  coast.  There  are  extensive  masses  in 
New  England  also.  The  Adirondacks  and  White  Mountains 
abound  in  varieties.  The  great  seaboard  cities  of  the  eastern 
coast — New  York,  Philadelphia,  Baltimore,  and  Richmond 
— are  built  on  gneiss.  In  the  western  part  of  the  Union  it 
forms  the  axes  of  extensive  mountain  chains,  and  the  centers 
of  raised  regions.  Gneiss  is  generally  a  highly  metamorphic 
sediment  that  has  sometimes  become  eruptive  (Scottish 
Highlands),  and  exhibits  contact  aureolae ;  also  metamor- 
phosed states  of  crushed  granites  and  other  acid  rocks 
(Alps,  north  shore  of  Lake  Superior,  etc.).  It  differs  from 


35°  MANUAL    OF  LITHOLOGY. 

granite  in  its  foliation  and  in  the  more  granular  texture  of 
the  ingredients,  which  are  not  interlocked  into  one  another, 
but  are  more  distinct,  and  occur  in  banded  and  foliated 
structures,  the  mica  laminae  and  other  unequiaxial  minerals 
(tabular  feldspars,  tourmaline,  hornblende,  lenticular  aggre- 
gations, concretions,  etc.)  having  a  parallel  arrangement 
which  allows  cleavage  along  the  foliation,  and  more  readily 
along  the  layers  of  mica.  The  feldspar  is  usually  orthoclase 
in  crystalline  grains  of  the  lighter  colors  of  the  granitic 
mineral,  except  the  decided  red,  which  is  only  found  when 
it  is  stained  with  ferric  oxide.  It  frequently  occurs  as 
phenocrysts  to  form  porphyritic  gneiss,  and  in  some  cases  is 
in  twinned  forms  half  a  foot  in  length.  Microcline  is  of  fre- 
quent occurrence,  and  sometimes  microperthite.  Plagio- 
clase  is  sometimes  greenish  from  epidotizing  of  pyroxenic 
ingredients.  Oligoclase  and  albite  are  common,  but  usually 
as  phenocrysts  and  not  in  the  general  mixture  ;  labradorite  is 
very  rare.  Quartz  occurs  in  grains  and  lenticular  strings, 
which  latter  sometimes  form  bands  of  great  purity  one  foot 
wide,  with  parallel  folia  of  mica  scattered  through  them. 
As  inclusions  in  quartz  occur  feldspar,  biotite,  fine  acicular 
rutile,  epidote,  zircon,  graphite,  etc.  Pegmatitic  structures 
occur  which  vary  from  the  ordinary  in  being  poikilitic,  as 
feldspar  is  highly  predominant.  As  in  granite,  the  mica  is 
muscovite  and  biotite  in  irregular  folia,  but  of  more  rounded 
contours.  Biotite  is  green,  with  inclusions  of  garnet,  epi- 
dote, zircon,  etc.,  and  alters  to  chlorite  and  epidote.  Musco- 
vite is  colorless  or  light  shades  of  green  and  gray.  As  stated 
under  the  description  of  minerals,  the  two  are  intergrown 
as  alternate  laminae  of  an  aggregation,  or  as  parts  of  the 
same  folia.  As  essentials  occur  tourmaline  in  prisms  and 
acicular  crystals,  single  or  aggregated,  and  sometimes  four 
inches  long  ;  occasionally  in  rounded  grains.  Hornblende 
occurs  in  biotite  gneiss,  and  is  associated  with  that  mineral 


METAMORPHIC  ROCKS.  35  I 

as  in  granite.  It  is  generally  of  light  colors,  or  not  of  very 
dark  ones.  Sometimes  glaucophane  is  found.  Pyroxene 
occurs  under  the  same  conditions  as  in  granite,  and  is  found 
in  plagioclase- gneiss  accompanied  by  few  accessories. 
Hypersthene  sometimes  occurs  with  labradorite  and  biotite* 
lolite  is  found  in  bluish  grains  and  forms  the  variety  "  cor- 
dierite  "-gneiss.  Garnet  is  one  of  the  most  common  acces- 
sories, and  is  more  abundant  (M)  than  in  granite,  but  much 
less  so  than  in  mica-schist.  It  shows  red  and  brown  colors.. 
Sillimanite,  fibrolite,  andalusite,  and  staurolite  are  abundant 
in  micaceous  gneiss,  but  less  so  than  in  mica-schist.  Less 
frequently  occur  epidote,  apatite,  zircon,  titanite,  magnetite, 
graphite,  chlorite,  etc.  Lenticular  aggregates  of  orthoclase 
or  microcline  alone,  orthoclase  with  mica  coating,  tourma- 
line and  quartz,  glaucophane  in  dark  blue  knots,  etc.,  also 
occur.  The  varieties  are  : 

(a)  Typical  Gneiss,  Mica-gneiss.  In  this  the  black  bisili- 
cate  is  one  or  both  of  the  micas.  Variations  are  muscovite-, 
biotite-,  and  muscovite-biotite-gneiss.  Predominant  mica  of 
either  kind  forms  micaceous  gneiss.  Variations  in  the  text- 
ure and  structure  of  the  mica  varieties  form  the  states 
known  as  granite-gneiss,  where  the  foliation  is  so  indistinct 
as  to  be  almost  lost ;  porphyritic-  or  augen-gneiss,  where 
phenocrysts  or  eye-shaped  kernels  of  feldspar  are  scattered 
through  the  mass ;  wood-gneiss,  where  the  ingredients  are 
arranged  in  fibrous-parallel  structure,  as  in  wood,  so  as  to 
supersede  the  schistose  structure  ;  slate-gneiss,  where  the 
texture  is  fine  and  mica  is  predominant,  so  that  a  decided 
cleavage  is  formed ;  ribbon  gneiss,  where  quartz,  feldspar, 
and  mica  are  aggregated  in  thin  and  mutually  alternating 
layers,  which  give,  on  a  cross-section,  the  striping  of  a  rib- 
bon ;  giant  gneiss  is  the  schistose  form  of  giant  granite, 
where  the  ingredients  are  respectively  an  inch  in  size  ;  red 
gneiss,  with  silica  74-76,  feldspar  orthoclase  and  predomi- 


352  MANUAL   OF  LITHOLOG  Y. 

nant,  mica  always  white  and  not  abundant ;  sometimes 
eruptive  ;  gray  gneiss,  with  silica  64-67,  mica  dark  and  pre- 
dominant, feldspar  orthoclase  and  oligoclase. 

(ft)  Cordterite-gneiss  is  a  variety  of  biotite-gneiss  where 
iolite  (cordierite)  is  abundant  with  gray  quartz  and  much 
feldspar.  It  is  usually  of  dark  color.  It  occurs  in  Saxonv, 
France,  Scandinavia,  etc.,  and  at  Guilford,  Conn. 

(c)  Granule-gneiss  has  little  mica,  and  that  usually  white. 
V.  Cotta  states  that  it  always  belongs  to  the  red  gneiss. 

Other  varieties  of  the  mica-gneisses  are  made  by  pre- 
dominant fibrolite,  garnet,  graphite,  epidote,  talc,  and  iron 
ores.  Where  the  mica  is  more  or  less  replaced  by  other 
minerals,  other  variations  of  greater  value  and  extent  occur, 
as: 

(d)  Sericite-g\\Q\ss  is  an  aggregate  of  quartz,  albite,  and 
sericite,  with  now  and   then  white  or  black  mica  in  small 
amounts,  and  a  chloride  mineral.     It  occurs  in  the  Taunus, 
in  Japan,  etc. 

(e)  Protogme-gneiss  is  a  decidedly  schistose  state  of  the 
schistoid  protogine-granite  already  noted.     It  consists  of  an 
aggregate  of  white  or  reddish  orthoclase,  greenish  white 
plagioclase,  and  quartz  with  a  talclike  mineral.     A  variety 
of  this  is  chloritic  gneiss.     It  is  widespread  in  the  Alps,  and 
was  called  "  alpenit  "  by  Simler. 

(/)  Hornblende-gneiss,  Syenite-gneiss,  etc.  This  is  a 
gneiss  with  hornblende  more  or  less  replacing  mica,  which 
is  biotite  rather  than  muscovite.  The  feldspar  also  changes, 
and  instead  of  predominant  orthoclase,  oligoclase  and  other 
plagioclases  appear.  With  orthoclase  we  have  "  syenite  "- 
gneiss,  with  plagioclase  "  diorite  "-gneiss,  and  with  plagio- 
clase and  mica  "  tonalite  "-gneiss.  Pyroxene  appears  in  this 
variety  and  alters  to  chlorite  and  epidote.  The  varieties  of 
hornblende-gneiss  are  very  abundant  in  the  Archaean  areas, 
and  the  Pennsylvania  gneiss  of  the  eastern  middle  part  of 


METAMORPHIC  ROCKS.  353 

the  State  is  granulite-hornblende-g\\eissy  with  accessory  allan- 
ite,  molybdenite,  and  considerable  magnetite,  which  forms 
•extensive  ores  in  New  Jersey.  Anthophyllite  and  glauco- 
phane  are  frequently  abundant  enough  to  form  varieties. 

(g)  Pyroxene-gneiss.  This  is  an  aggregate  of  predomi- 
nant plagioclase(albite,  oligoclase,  labradorite,  and  anorthite) 
with  some  orthoclase  and  quartz  and  a  light-colored  pyrox- 
ene. As  accessories  are  wollastonite,  scapolite,  occasional 
calcite,  biotite,  garnet,  titanite,  and  frequently  hornblende. 
Occasional  combinations  are  omphacite  and  bronzite,  saus- 
.suritic  feldspar,  etc.  This  variety  can  be  called  from  its 
feldspar  plagioclase-gueiss  and  anvrt  kite-gneiss,  and  when  the 
pyroxene  is  hypersthene  it  may  be  called  "  norite  "-gneiss  ; 
when  diallage,  "  gabbro  "-gneiss  ;  when  augite,  "  diabase  "- 
gneiss  ;  or  all  the  minerals  can  be  used  as  a  prefix,  as  hyper- 
sthene-anomiteplagioclase-giiQiss,  diallage-gneiss,  augite-gneiss, 
wollastonite -augite- gneiss,  scapolitic  augite-gneiss.  Augite- 
gneiss  is  found  in  Scandinavia,  Spain,  Bretagne,  Vosges, 
etc.,  and  in  Minnesota,  Wisconsin,  and  New  York. 

QUARTZ-FELDSPAR-MICA   GROUP. 

HALLEFLINTA. 

A  (M)  compact  homogeneous  rock  with  an  appearance 
like  hornstone,  a  splintery  to  conchoidal  fracture,  and 
color  varying  in  bands  of  gray,  green,  yellow,  dark 
brown,  to  black.  It  fuses  only  on  thin  edges.  It  may 
be  considered,  in  some  cases,  as  a  compact  gneiss,  in 
others  as  a  devitrified  rhyolite. 
Silica  61-83  5  Gr.  2.65-2.78. 

This  occurs  in  Sweden  with  granulite  and  gneiss,  into 
which  it  can  at  times  be  traced,  but  Nordenskiold  has  re- 
cently  described  occurrences  of  it  as  a  devitrified  rhyolite, 
where  it  exhibits  the  flow  structure,  lithophysas,  etc.,  of  that 


354  MANUAL   OF  LITHOLOGY. 

rock.  It  is  fine-crystalline  (m),  and  shows  an  intimate  mix- 
ture of  quartz  and  feldspar,  with  scales  of  mica  and  chlorite. 
We  have,  therefore,  two  origins  for  the  same  rock — the 
metamorphic  form  of  fine  sediments  which  have  become 
a  compact  gneiss,  and  the  devitrified  form  of  an  extrusive 
glass.  Halleflinta  much  resembles  adinole  and  porphyroid. 
A  porphyritic  halleflinta  was  found  to  be  a  devitrified  quartz- 
porphyry.  It  is  also  found  in  Bavaria,  Baden-Baden,  and 
the  northwestern  part  of  South  America. 

PORPHYROID. 

A  rock  with  felsitic  groundmass;    somewhat  schistose 
from  the  development  of  micaceous  scales,  and  exhib- 
iting sporadic  phenocrysts  of  quartz  and  feldspar. 
Silica  75-83  ;  Gr.  2.6-2.75. 

It  is  found  among  the  schistose  rocks  of  Saxony  and  in 
the  Paleozoic  areas  of  other  parts  of  Europe,  and  is  thought 
to  be  an  orogenic  product  from  extensive  shearing  and  sub- 
sequent rearrangement  of  material.  It  resembles  a  schistose 
and  micaceous  quartz-porphyry,  and  is  like  adinole  in  its 
appearance  and  behavior.  The  feldspar  is  orthoclase  or 
albite  in  quite  perfect  crystals,  and  the  quartz  is  frequently 
in  double  pyramids.  The  mica  is  paragonite  or  sericite 
(both  belonging  to  muscovite).  With  a  coarser  grain  the 
rock  would  become  a  highly  crystalline  gneiss.  It  so  much 
resembles  the  rock  last  noted  that  some  authorities  call  it  a 
"  porphyritic"  halleflinta.  It  occurs  in  the  northern  penin- 
sula of  Michigan  in  the  Huronian  formation,  and  in  Nevada. 


METAMORPHIC  ROCKS,  35 S 

BASIC  SERIES. 

The  rocks  of  this  series  are  more  or  less  foliated,  crystal- 
line-granular, generally  (M)  compounds  of  pyroxene, 
amphibole,  garnet,  talc,  chlorite,  serpentine,  with 
feldspar  (usually  plagioclase),  quartz,  and  various  ac- 
cessories ;  coarse-  and  fine-grained,  and  (M)  compact ; 
massive  or  fissile ;  variously  colored. 
Silica  26-58  ;  Gr.  2.7-3.5. 

They  can  be  divided,  according  to  the  predominant  min- 
erals, as  follows : 

MARGAROPHYLLITE  GROUP: 

Talc-schist,  calcereous  talc-schist,  listwenite,  dolerine,  renssel- 

aerite,  steatite,  potstone,  chloride  potstone. 
Chlorite-schist,  uralite-schist,  chloritoid-schist. 
Pyrophyllite-schist. 

EPIDOTE  GROUP  : 

Epidosite,  epidote-schist. 

GARNET  GROUP  : 

Garnet  rock,  eclogite,  cyanite  rock,  kinzigite. 

AMPHIBOLE  GROUP  : 

Amphibolite,  hornblende-schist,  actinolite-schist,  glaucophane- 
schist,  green  schist. 

PYROXENE  GROUP : 

Pyroxene  rock,  pyroxene-schist,  erlan. 

OLIVINE  GROUP  : 

Olivine  rock,  olivine-schist,  eulysite. 

MARGAROPHYLLITE   GROUP. 

TALC-SCHIST. 

A  schistose  aggregate  of  talc  with  quartz  and  (less  fre- 
quently) feldspar,  and  other  accessories,  the  talc  is 
predominant  in  yellowish  or  greenish  scales ;    soft  ; 
with  pearly  luster  and  greasy  feel.  J^  vt^/ 
Silica  27-62  (average  50-55) ;  Gr.  2.6-2.8. 


MANUAL    OF  LITHOLOGY. 

This  occurs  in  beds  of  considerable  size,  but  not  very 
widely  spread,  and  is  found  in  the  Urals,  Alps,  Apennines, 
in  Brazil,  Canada,  New  England,  and  along  the  Archaean 
formation  of  the  Atlantic  coast.  Quartz  occurs  in  grains, 
lenticules,  and  strings  parallel  to  the  foliation.  Other  acces- 
sories are  micas,  chlorite,  actinolite,  calcite  and  other  car- 
bonates, magnetite,  pyrite,  and,  less  commonly,  garnet, 
olivine,  tourmaline,  asbestus,  rutile,  cyanite,  staurolite,  and 
others.  It  is  a  metamorphosed  sediment,  and  shades  into 
protogine-gneiss,  chlorite-schist,  clay-slate,  mica-schist,  and 
similar  rocks.  As  varieties  are  : 

(a)  Calcareous  talc-schist.      This  bears  to  this  rock  the 
same  relation  that  calcareous   mica-schist  bears   to   mica- 
schist.     It  is  a  less  common  rock,  but  is  found  in  similar 
formations,  as  along  the  Green  Mountains,  in  New  England, 
etc. 

(b)  Listwenite   is  a  granular  talc-schist,   with  yellowish 
greenish  color,  from  the  Urals,  and  carrying  much  quartz 
and  calcite,  so  that  it  shows  a  fine-granular-slaty  structure. 
With  the  calcite  is  dolomite,  and  sometimes  siderite.     In 
some  varieties  the  quartz  fails.     This  is  the  rock  penetrated 
by  beresite. 

(c)  Dolerine  (Jurine)  is   a  talc-schist   from    the    Pennine 
Alps  with  essential  feldspar  and  chlorite. 

(d)  Rensselaerite  (Emmons)  is  a  pseudomorph  of  talc  after 
pyroxene  that  is  found  in  northern  New  York  and  Canada, 
especially  at  Hermon,  N.  Y.     It  is  associated  with  crystal- 
line limestone,  and  shades  imperceptibly  into  serpentine.     It 
is  seldom  found  in  large  masses :    they  are  irregular  and  up 
to  900  to  1000  feet  long.     It  is  cryptocrystalline  and  waxlike 
in  composition,  with  colors  whitish,  yellowish,  gray,  green- 
ish, and  pearl-white. 

(e)  Steatite,  Soapstone,  is  a  massive  talc,  coarse-granular, 
grayish  green,  gray,  and  brownish  gray.     This  frequently 


METAMORPHIC  ROCKS.  357 

contains  chlorite,  and  then  forms  what  some  authorities  call 
"  talcose  potstone."  One  of  the  principal  quarries  in  the 
United  States  is  a  few  miles  northwest  of  Easton,  Pa.;  an- 
other is  near  Philadelphia  in  the  same  State. 

(/)  Potstone  is  a  soft,  sectile,  greenish  gray  aggregate  of 
talc,  chlorite,  and  serpentine  in  a  feltlike  web.  It  is  rarely 
foliated.  It  is  infusible,  and  frequently  carries  as  accessories 
mica,  calcite,  dolomite,  magnetite,  and  pyrite.  These  some- 
times cause  effervescence  with  acids.  It  is  an  impure  stea- 
tite, and  is  found  in  New  England,  Canada,  and  New  York. 
It  is  used  for  making  cooking-pots,  and  was  so  used  by  the 
Indians. 

(g)  Chloritic  Potstone  is  a  variety  that  carries  predomi- 
nant chlorite,  and  is  therefore  a  transition  to  that  mineral. 
It  is  found  with  steatite. 

CHLORITE-SCHIST. 

A  granular  to  schistose  aggregate  of  scaly  chlorite  with 
quartz,  and  sometimes  feldspar,  talc,  mica,  epidote, 
and  magnetite. 

Silica  26-50;  Gr.  2.7-3. 

This  occurs  with  gneiss  and  other  schists  in  bedded 
masses,  arid  is  found  in  Austria,  the  Alps,  Tyrol,  Italy,  Asia 
Minor,  the  Urals,  Brazil,  Transvaal,  and  in  the  Southern 
Atlantic  States.  The  chloritic  mineral  is  one  of  that  group, 
and  is  predominant.  It  gives  the  green  or  blackish  green 
color  and  grayish  green  streak  to  the  rock.  It  is  usually 
soft  and  coarsely  foliated,  and  with  little  quartz.  Abundant 
quartz  forms  a  more  granular  rock  with  greater  hardness, 
and  sometimes  occurs  in  folia,  lenticules,  irregular  strings, 
or  thin  veins  that  traverse  the  rock  in  all  directions.  It 
shades  into  talc-schist,  protogine-gneiss,  argillaceous  mica- 
schist,  and  slaty  serpentine.  The  coarser  schistose  states 


35$  MANUAL   OF  LITHOLOGY. 

are  sometimes  called  chloritic  gneiss,  while  the  finer  and  more 
even  and  silky  kinds  are  chlorite- slate. 

(a)  Uralite-schist  (Kantkiewicz)  is  a  coarse-schistose  aggre- 
gate of  (m)  fine-grained  chlorite  and  epidote  with  accessory 
quartz  and  biotite,  and  with  (M)  phenocrysts  of  augite-like 
uralite.     It  alters  to  a  green  chloritic  mineral.     It  is  found 
in  the  Urals. 

(b)  Chloritoid  Schist  (Sterry  Hunt)  is  a  dark- colored  schist 
of  considerable  extent  in  Canada,  composed  of  a  chloritoid 
mineral  allied  to  chlorite  and  to  ottreiite.     It  also  occurs 
near  Salzburg,  and  in  Roumania. 

PYROPHYLLITE-SCHIST. 

A  compact  and  but  slightly  schistose  aggregate  of  pyr- 
ophyllite. 

Silica  65.93  ;  Gr.  2.82-2.91. 

This  is  a  rare  occurrence  as  a  rock,  and  is  found  thus  in 
North  and  South  Carolina,  Georgia,  and  Arkansas,  where  it 
forms  schistose  to  compact  beds  of  greenish  to  yellowish 
white  color,  resembling  in  appearance  and  feel  a  slaty  soap- 
stone.  It  is  generally  free  from  accessories,  and  forms  a 
smooth  and  evenly  soft  rock,  microcrystalline  to  aphanitic, 
that  is  extensively  worked  for  slate  pencils. 

EPIDOTE   GROUP. 

EPIDOSITE  (Pistacite  Rock). 

A  yellowish  green,  light  green,  to  dark  green  aggregate 
of  predominant  epidote  and  quartz,  with  an  amphi- 
bole,  mica,  or  chlorite,  and,  less  frequently,  feldspar 
and  pyroxene ;  hard  ;  massive  to  schistose ;  granular 
to  compact ;  tough. 

Silica  62 ;  Gr.  3-3.4 ;  H.  7. 

It  occurs  associated  with  crystalline  schists,  and  also  as 
an  alteration  product  from  an  eruptive,  and  is  found  in 


METAMORPHIC  ROCKS,  359 

Brazil  (?),  at  several  localities  in  Canada  (St.  Joseph,  Grand 
Manatee  River,  Melbourne),  Greece,  island  of  Anglesea,  etc., 
and  as  the  alteration  product  of  a  melaphyre  in  northwestern 
South  America.  It  is  also  reported  from  Portage  Lake, 
Wis.,  as  a  similar  product.  The  Canadian  textures  are  com- 
pact to  coarse-grained.  The  varieties  are  : 

(a)  Gtaucofl/iane-epidosite.     From  the  island  of  Syra,  with 
a  yellowish  white  principal  mass  of  fine  epidote,  with  zoisite, 
mica,  and  chlorite,  in  which  are  somewhat  stout  glauco- 
phanes. 

(b)  Omphacite-zoisite  Rock,  from  the  same  island,  has  the 
principal    mass   of   grains   of   zoisite    with    phenocrysts   of 
omphacite,  and  as  accessories  are  leaves  of  talc,  grains  of 
epidote,  stout  prisms  of  tourmaline,  folia  of  chlorite  and 
biotite,  and  (ni)  rutile  and  calcite. 

EPIDOTE-SCHIST. 

A  schistose  aggregate  of  the  above  minerals  with  similar 
silica,  specific  gravity,  and  other  characteristics. 

This  is  associated  with  the  above  rock,  and  forms  transi- 
tions into  it.  The  variety  of  the  island  of  Timor  shows  as 
accessories  sericite,  magnetite,  quartz,  calcite,  plagioclase, 
and  specular  hematite,  and  has  a  greenish  color  and  silvery 
luster  on  the  foliation  surfaces.  As  varieties  are : 

(a)  ffvrnbtende-epidote-schist.     From  the  phyllite  forma- 
tion of  the  peninsula  of  Chalcidice.      It  is  a  fine-grained 
aggregate  of  coarse  epidote,  bright  green  hornblende,  and 
tufts  of  chlorite. 

(b)  Mtca-epidote-schist,  in  dark-green  thin  foliated  struc- 
ture, with  predominant  epidote,  quartz,  green  biotite,  and 
iron  ores,  with  variations  where  quartz  and  mica  were  each 
predominant. 

(c)  Calcareous     Epidote  -  schist,     "  Kalkpistacit  "  -  schist 
(Forth).     From  northeast  Bohemia,  with  a  principal  mass 


MANUAL   OF  LITHOLOG  Y. 

of  calcite,  epidote,  and  mica,  with  accessory  albite,  quartz, 
iron  ores,  and  pyrite.  This  is  the  parallel  of  calcareous 
mica-schist,  etc. 

(d)  Murasaki  (Koto),  Manganese-epidote-schist,  from  the 
island  of  Shikoku,  Japan,  is  a  violet  rock  of  small  quartz 
grains  with  phenocrysts  of  epidote  f  inch  long,  with  acces- 
sory sericite,  greenish  yellow  garnet,  rutile,  orthoclase,  and 
blood-red  specular  hematite.  These  are  called  also  "  pied- 
montite  "-schists,  from  the  name  of  the  manganese-epidote, 

GARNET   GROUP. 

GARNET  ROCK,  Garnetyte  (Dana). 
A  crystalline-granular  aggregate  of  predominant  garnet 
with  an  amphibole,  augite,  epidote,  quartz,  and  mag- 
netite ;  variously  colored. 

Silica  44.85  ;  Gr.  3.3-3.54. 

It  is  a  rare  rock,  and  occurs  in  a  few  irregular  beds  and 
lenticular  masses  in  mica-schist  and  gneiss,  and  is  found  in 
Bohemia,  Saxony,  Silesia,  Tyrol,  France,  the  Urals,  Belgium, 
Canada,  and  Nevada.  With  the  failure  of  garnet  this  be- 
comes amphibolite.  In  addition  to  the  above  minerals  there 
are  also  found  with  garnet  in  smaller  proportions  and  less 
frequently  micas,  iron  ores,  serpentine,  apatite,  olivine, 
vesuvianite,  calcite,  pyrite,  and  now  and  then  feldspar. 
Zirkel  notes  the  infrequency  of  the  latter  as  peculiar.  Owing 
to  the  great  variety  of  its  mixtures  the  color  varies  widely. 
Sometimes  the  brown  or  yellowish  garnet  (aplombe)  pre- 
dominates, so  that  the  rock  consists  almost  wholly  of  that 
mineral.  It  is  usually  of  that  color,  buff,  or  greenish  white  ; 
tough  ;  fine-grained.  The  stone  of  that  color  from  Viel 
Salm,  Belgium,  forms  the  best  oil-stone  in  the  world.  It  is 
there  a  spessartite  (manganese-garnet).  At  Orford,  Canada, 
a  white  lime-alumina-garnet  (grossularite)  forms  with  a  little 


METAMORPHIC  ROCKS.  361 

serpentine  a  whitish  rock.  At  St.  Frangois,  Canada,  the 
same  garnet  forms  with  an  almost  equal  proportion  of  pyr- 
oxene a  yellowish  white  to  greenish  white  rock.  At  Hohen 
Waid  in  the  Odenwald  a  beautiful  brown  garnet  forms  a 
rock  with  quartz,  calcite,  actinolite,  and  epidote.  At  Big 
Cottonwood  Canon,  Utah,  a  similar  rock  is  formed  of  brown 
garnet,  quartz,  (m)  epidote,  and  folia  of  iron. 

ECLOGITE  (Hauy). 

A  coarse-  to  fine-grained  (seldom  compact)  crystalline- 
granular  aggregate  of  grass-green  omphacite  (or 
diopside)  and  red  garnet  with  frequent  blue  cyanite 
and  white  mica.  The  first  occurs  as  a  crystalline 
matrix,  usually  slaty  or  fibrous,  in  which  the  garnets 
appear  as  phenocrysts. 

Silica  45-57;  Gr.  3.20-3.50. 

This  occurs  in  quite  extensive  lenticular  beds  in  gneiss, 
granulite,  serpentine,  and  mica-schist,  and  is  found  in  the 
Erzgebirge,  Fichtelgebirge,  Austria,  Baden,  Scotland,  the 
western  Alps,  Norway,  Sweden,  Servia,  the  island  of  Syra,. 
Japan,  the  Orange  Free  State,  at  Cape  Horn,  and  a  some- 
what similar  rock  is  found  in  the  Sierra  Nevadas.  Ompha- 
cite is  found  in  short,  thin  leek-green  or  grass-green  prisms, 
which  are  sometimes  serpentinized.  The  garnet  is  almandite 
with  variations  in  the  proportions  of  the  ferrous  and  ferric 
oxides.  It  occurs  in  rounded  phenocrysts.  Cyanite  is 
usually  (M) ;  sometimes  only  (m) ;  frequently  so  predominant 
that  it  forms  the  following  variety.  Quartz  is  generally 
allotriomorphic,  and  sometimes  as  large  as  peas.  Black 
hornblende  is  usually  present,  and  sometimes  exceeds  the 
omphacite  and  garnet,  so  as  to  form  an  eclogitic  amphibolite. 
In  some  varieties  grass-green  smaragdite  appears  with 
omphacite,  and  alters  to  chlorite.  The  silvery  mica  is  mus- 
covite.  Biotite  now  and  then  occurs.  Zoisite,  rutile,  apa- 


362  MANUAL   OF  LITHOLOGY. 

tite,  magnetite,  pyrite,  pyrrhotite,  and  zircon  also  occur 
quite  predominantly.  This  rock  is  a  hard  and  dense  mix- 
ture that  resists  weathering  better  than  its  surroundings, 
and  projects  from  them  in  prominent  knolls. 

(a)  Cyanite  Rock  is  a  variety  of  the  above  where  cyanite 
is  predominant.  It  consists  of  an  aggregate  of  cyanite  and 
white  mica,  and  also  occurs  as  an  offshoot  of  mica-schist. 
As  the  latter  it  is  common  in  the  Green  Mountains  of  Ver- 
mont. The  cyanite  is  of  varying  color,  from  fine  blue  to 
white,  and  usually  occurs  in  long,  flat,  bladed  crystals,  and 
so  predominant  that  the  rock  is  almost  entirely  composed 
of  it.  As  accessories  occur  garnet,  calcite,  and  occasionally 
tourmaline. 

KINZIGITE  (Fischer). 

A  crystalline-granular  schistose  aggregate  of  garnet, 
biotite,  and  oligoclase ;  coarse  to  compact.  A  garnet- 
gneiss. 

Silica  44.53;  Gr.  3. 

This  occurs  associated  with  gneiss  and  crystalline  schists 
in  the  Black  Forest  (where  it  was  first  noted  at  the  Kinzig), 
the  Odenwald,  and  in  Italy.  The  first  is  coarse-schistose, 
and  the  ingredients  of  large  size.  Oligoclase  is  white  and 
grayish  green,  and  frequently  half  an  inch  in  size.  It  is 
sometimes  accompanied  by  orthoclase  and  microcline. 
Garnet  is  sometimes  as  large  as  peas.  Biotite  is  black,  and 
when  quartz  appears  it  forms  a  garnetiferous  biotite-gneiss. 
Quartz  is  not  common,  and  occurs  in  grains  and  flat  lenti- 
cules.  As  accessories  occur  graphite,  apatite,  pyrite,  mag- 
netite, iolite,  sillimanite,  fibrolite,  and  rutile. 


METAMORPHIC  ROCKS.  363 

AMPHIBOLE   GROUP. 

AMPHIBOLITE. 

A  granular  aggregate  of  dark  green  to  black  hornblende 
with  more  or  less  quartz,  and  sometimes  chlorite. 
Silica  47-50  ;  Gr.  2.9-3.1. 

This  occurs  in  beds  and  flat  lenticular  masses  with  gneiss, 
mica-schist,  and  phyllite,  and  is  found  in  Saxony,  Silesia, 
Japan,  New  England,  Nevada,  etc.  The  hornblende  is  fre- 
quently the  sole  ingredient.  As  accessories  in  addition  to 
those  given  are  biotite,  orthoclase,  plagioclase,  garnet,  pyr- 
oxene, zoisite,  and  iron  ores.  These  tend  to  form  variations 
from  the  schistose  variety,  and  from  hornblende-gneiss.  In 
amphibolite  there  is  no  tendency  to  foliation,  and  the  in- 
gredients are  arranged  irregularly  throughout  the  mass. 

/v/^r/ar-amphibolite,  Plagioclase-amphibolite,  is  a  vari- 
ety with  considerable  plagioclase  (and  some  orthoclase), 
so  that  it  forms  a  ^ta-diorite  (Dana).  It  is  not  common 
without  foliation.  Other  varieties  noted  by  different 
authorities  are  quartz-,  epidote-,  garnet-,  and  £tf/«V^-amphibolite. 
The  last  has  been  already  described  under  its  original  name, 
Jiemithrtne. 

HORNBLENDE-SCHIST. 

A  granular  and  schistose  aggregate  of  the  above  min- 
erals with  similar  silica  and  specific  gravity. 

This  is  a  more  widespread  rock  than  the  former,  as  it  is 
associated  with  schists  and  partakes  of  their  foliation.  It  is 
common  in  western  New  England,  and  the  garnetiferous 
variety  of  the  region  running  north  and  south  along  the 
Connecticut  River  between  Norwich,  Vt.,  and  Hanover, 
N.  H.,  has  been  well  known  for  many  years  as  furnishing 
transparent  garnet  fit  for  jewelry.  Coarse  garnets  much 
fissured  are  found  as  large  as  filberts,  but  with  bright  red- 


364  MANUAL   OF  LITHOLOGY. 

dish  brown  color.  The  garnetiferous  mica-schist  of  the 
Green  Mountains  frequently  contains  a  considerable  amount 
of  calcite  intimately  mixed  with  it,  so  that  the  rock  weathers 
to  a  rough  surface,  and  the  imperfect  garnets  in  spheroids 
of  the  size  of  French  peas,  or  smaller,  project,  to  give  the 
rock  a  pitted  appearance.  Other  accessories  are  epidote, 
biotite,  scapolite,  and  zoisite,  as  well  as  those  named  above. 
In  some  cases  the  quartz  and  hornblende  are  aggregated  in 
flakes  or  patches,  so  that  the  rock  has  a  beautifully  mottled 
appearance.  The  appearance  of  feldspar  forms  a  transition 
to  hornblende-gneiss.  The  hornblende-granulite  of  the 
South  Mountain  in  eastern  Pennsylvania  abounds  in  segre- 
gations of  this  rock  with  predominant  hornblende,  and 
also  intercalated  masses  of  hornblende-gneiss.  In  the  Lake 
Superior  region  and  in  the  Alps  are  dikes  of  diabase  altered 
to  this  rock  by  squeezing,  and  in  Calaveras  County,  Cal., 
olivine  extrusives  have  been  altered  in  a  similar  manner  to 
form  ta/£-amphibole-schist.  Much  oligoclase  forms  diorite- 
schist. 

ACTINOLITE-SCHIST. 

A  schistose  aggregate  of  actinolite,  either  alone  or  with 
other  minerals. 

Silica  52-55  ;  Gr.  2.95-3.05. 

This  occurs  like  hornblende-schist,  and  is  found  in  the 
Fichtelgebirge,  the  Alps,  Italy,  and  along  the  Green  Mount- 
ains. The  accessories  are  generally  subdominant  to  actino- 
lite. They  are  quartz,  feldspar,  epidote,  garnet,  biotite, 
muscovite,  chlorite,  monoclinic  pyroxene,  rhombic  horn- 
blende, zoisite,  olivine,  the  iron  ores,  zircon,  and  pyrite. 
Ollenite  is  an  ^akte-actinolite-schist  that  forms  at  Monte 
Rosa  a  large  mass,  which  varies  from  schistose  to  compact. 


METAMORPHIC  ROCKS.  365 

GLAUCOPHANE-SCHIST,  Glaucophanyte (Dana). 

A  schistose  aggregate  of   glaucophane   with  accessory 
epidote  and  muscovite. 
Silica  55-57;  <Jr-  3- 

This  occurs  in  thin  lenticules  with  other  schists,  and  is 
found  in  the  island  of  Syra,  Switzerland,  Piedmont,  New 
-South  Wales,  Bretagne,  and  California.  The  glaucophane 
is  in  blue  acicular  crystals  with  parallel  arrangement,  so 
that  the  mineral  has  been  taken  for  cyanite.  As  accessories 
occur  green  mica,  hornblende,  zoisite,  quartz,  plagioclase, 
arfvedsonite,  rutile,  chlorite,  and  iron  ores.  A  fourchite- 
sandstone  contact  near  San  Francisco,  CaL,  formed  glauco- 
phane-schist. 

j£/z#0te-glaucophane-schist  is  a  variety  where  epidote  is 
predominant.  It  is  found  in  Switzerland,  Piedmont,  Croatia, 
Spain,  Greece,  and  in  Asia  Minor.  Predominant  epidote 
forms  glaucophane-epidote-schist. 

(NOTE  on  Amphibole-schists.  These  are  thought  by 
many  authorities  to  have  been  basic  intrusions  in  the  rocks 
where  they  are  found,  and  that  they  have  been  altered  with 
those  rocks  to  their  present  state.  It  may  also  be  noted 
that  in  some  localities  garnet,  when  finely  crystalline,  is  in 
trapezohedra  rather  than  dodecahedra. 

GREEN  SCHIST  (Kalkowsky). 

A  green,  grayish  green,  to  greenish  black  schistose  ag- 
gregate of  quartz  and  feldspar  in  varying  proportions, 
with  changeable  amounts  of  hornblende,  epidote,  and 
chlorite. 

This  is  held  by  many  authorities  to  be  a  squeezed  dia- 
base. It  is  found  in  regions  of  erogenic  movements  with 
phyllite,  and  sometimes  in  considerable  masses,  and  is  found 
in  the  Alps,  Silesia,  Saxony,  Lake  Superior,  etc.  Feldspar 


366  MANUAL   OF  LITHOLOGY. 

and  quartz  are  the  predominant  minerals,  and  form  a  closely 
intercrystalline  background  for  the  other  minerals.  The 
hornblende  is  light  green,  greenish  blue,  and  blue,  and  forms 
long  thin  prisms.  Epidote  is  usually  a  secondary  form  of 
hornblende  and  chlorite.  With  these  occur  black  augite 
(sometimes  altered  to  viridite  and  epidote),  calcite,  and  the 
ores* 

(a)  Prasinite  (Kalkowsky)  is  a  similar  aggregate  of  horn- 
blende,  epidote,   and    chlorite    6f    intensely   green    color,. 
whence  the  name. 

(b)  Amphibole-adinole-sc\\ist  is  a  granular  to  compact  felsitic 
rock  like  adinole,  with  a  light  green  to  greenish  gray  color 
and   schistose   structure,   from    Saxony.      It    is    Credner's 
"  hornschiefer."     The  composition  is  (m)  generally,  as  it  is 
seldom  that  it  is  coarse-grained  enough  to  distinguish  the 
ingredients  without  a  strong  lens.     It  is  formed  of  quartz, 
plagioclase,  hornblende,  epidote,  and  magnetite. 

PYROXENE  GROUP 

PYROXENE  ROCK. 

A  granular  to  compact  aggregate  of  predominant  pyrox- 
ene without  schistose  structure,  with  or  without 
accessories.  Silica  and  specific  gravity  are  as  in  the 
mineral  group,  with  variations  on  both  sides. 

This  occurs  with  the  crystalline  schists  with  changeable 
character  (from  variation  in  the  predominant  mineral).  It 
never  plays  as  large  a  part  as  the  corresponding  amphibole 
rock.  The  varieties  are  : 

(a)  Enstatite  Rock.  From  Bavaria,  the  Transvaal,  and  in 
Delaware  and  Lancaster  counties,  Pa.  As  accessories  are 
magnetite,  picotite,  olivine,  diopside,  rnagnesite,  and  mono- 
clinic  pyroxene.  Silica  53-55  ;  Gr.  3.22. 


METAMORPHIC  ROCKS. 

(b)  Sagvandite  (Pettersen)  is  a  similar    rock  from  Norway 
composed  of  enstatite  and  magnesite.     Silica  55  ;  Gr.  3.22. 

(c)  Diallage-hypersthene  Rock  is  a  fine-grained  aggregate 
from  Madagascar. 

(d)  Augite  Rock  forms  a  granular  green  and  yellow  ag- 
gregate  in  the   mica-schist   of  western    Massachusetts.     It 
occurs  also  in  Scandinavia  and  Canada. 

(e)  Malacolite  Rock  forms  a  white  granular   and   almost 
compact  rock,  with  splintery  to  earthy  fracture,  in  a  bed  in 
the  granular  limestone  of  the  Riesengebirge  and  in  Sweden. 
This  is  the  "  pyroxenite  "  of  Coquand.     It  affords  silica  55. 

(/)  Omphacite  Rock,  in  large  irregular  grains,  with  spo- 
radic grains  of  olivine  and  rutile,  is  found  in  the  Sierra 
Guadarrama. 

(g)  Diallage  Rock  is  a  light-green,  compact  aggregate  of 
diallage,  with  columnar  jointing,  from  Cyprus,  where  it  is 
associated  with  gabbro  and  serpentine.  The  diallage  is 
visible  with  a  lens,  and  is  associated  with  talc,  serpentine, 
and  tremolite. 

(Ji)  £0&&*-diallage  Rock,  from  the  peninsula  of  Chalcidice, 
is  an  aggregate  of  dark-colored  diallage  and  white  lustrous 
grains  of  zoisite.  As  accessories  are  a  talcose  mineral  and 
a  monoclinic  feldspar.  It  forms  a  beautiful  rock  with  coarse 
granitic  structure.  The  diallage  is  somewhat  altered  to 
green  fibrous  hornblende. 

PYROXENE-SCHIST. 

A  similar  aggregate  to  pyroxene  rock  with  a  schistose 
structure. 

This  is  somewhat  more  rare  than  the  pyroxene  rock,  as 
the  alterations  that  produce  foliation  generally  alter  the  rock 
to  hornblende,  so  that  the  altered  states  are  found  under  the 
amphibole-schists.  The  silica  and  specific  gravity  are  as 
above  given.  The  varieties  noted  are : 


368  MANUAL   OF  LITHOLOGY. 

(a)  Augtte-schist  is  a  fine-grained  schistose  aggregate  of 
pale  or  dark  green  augite,  Avith   sometimes  quartz,  plagio- 
clase,  magnetite,  and  chlorite,  of  rare  occurrence  in  the  crys- 
talline schists.     In  some  cases  they  are  compact,  soft,  and 
readily  scratched  with  the  finger-nail.     They  are  so  com- 
pact that  only  augite  can  be  noted  with  a  lens.     Much  pla- 
gioclase  forms  diabase-schist. 

(b)  Gtauctf/iane-augite-schist,  which  varies  between  dial- 
lage  and  omphacite  in  its  augite  content  is  reported  from 
the  island  of  Syra. 

(c)  Vesuvtamte-augite-schist  is  reported  from  Elster  as  a 
thick-banded  dirty  green  or  dirty  white  rock,  in  lenticules 
in  gneiss,  composed  of  quartz,  garnet,  and  augite,  with  vesu- 
vianite,  plagioclase,  apatite,  titanite,  and  pyrite.     Generally 
<«). 

(d)  Egeran-schist,  Vesuvianite-schist,  is  a  schistose  aggre- 
gate   of   vesuvianite,    augite,    tremolite,  and    quartz.     This 
occurs  near  Eger,  Bohemia,  and  was  first  thought   to  be 
eclogite.     It  consists  of  predominant  vesuvianite  which  ob- 
tained its  name  "  egeran  "  from  this  locality,  where  this  rock 
lies  in  an  isolated  mass  in  granite. 

ERLAN  (Breithaupt). 

A   crystalline-granular   aggregate    of    almost    colorless 
pyroxene  in  irregular  grains  or  fibers,  with  colorless 
and  limpid  feldspar,  vesuvianite  (m),  quartz,  epidote, 
rutile,  titanite,  biotite,  and  muscovite. 
Silica  53.16;  Gr.  3--3.I. 

This  occurs  an  beds  in  gneiss,  and  is  found  at  Erla 
(whence  the  name)  near  the  Schwarzenberg.  It  is  usually 
a  compact  felsitic  mass  with  light  greenish  gray  color,  ap- 
pearance like  saussurite,  and  fine-splintery  fracture.  It  was 
thought  by  Breithaupt  to  be  of  an  entirely  different  compo- 
sition. 


METAMORPHIC  ROCKS.  369 

OLIVINE    GROUP. 

OLIVINE  ROCK. 

A  yellowish  green  to  dark  green  aggregate  of  granular 
olivine  irregularly   arranged,   and   with   or   without 
accessories,  but  without  foliation. 
Silica  29-41  ;  Gr.  2.7-3.3. 

This  occurs  in  many  varieties  interlaminated  with  gneiss, 
mica-schist,  hornblende-schist,  talc-schist,  granulite,  etc. 
It  is  a  rare  combination  and  usually  altered  to  serpentine. 
The  bands  and  masses  are  irregular  and  of  subordinate  ex- 
tent, and,  as  stated  by  Geikie,  were  "  probably  eruptive 
masses  contemporaneous  with  or  subsequent  to  the  sur- 
rounding gneisses  and  schists."  Olivine  rarely  occurs  alone, 
but  is  combined  with  one  of  the  pyroxenes.  It  alters  to  ser- 
pentine and  talc.  The  varieties  are  : 

(a)  Enstatite-Q\\vi\\Q  Rock,   with  diopside,    green    clino- 
chlore,  and  magnetite,  in  a  bed  in  the  Fichtelgebirge  with 
hornblende-gneiss.     It  alters  to  talc-schist.     It  is  also  found 
in  Austria  and  Sweden. 

(b)  Bronzite-oliv'me  Rock,  from  Austria,  between  diorite- 
schist  and  biotite-gneiss,  consisting  of  olivine  and  actinolite 
in  which  the  bronzite  occurs  as  phenocrysts.     Spinel,  ser- 
pentine, magnetite,  and  chlorite  also  occur. 

(c)  Amphibole-o\i\\nQ  Rock,  from  Himberg,  Austria,  with 
olivine  forming  one  third  of  the  mass,  the  rest  being  actino- 
lite, hypersthene,  dark  green  spinel,  clinochlore,  and   talc. 
The  weathered  crust  shows  amphibole  and  anthophyllite. 
It  occurs  also  in  Sweden. 

(d)  Garnet-Q\\v'me  Rock,  in  granulite  of   the    Kampthal, 
Austria,  is  composed  of  olivine,  picotite,  pyrope,  bronzite, 
hornblende,  and  scanty  diallage  in  a  coarse  mixture. 

(e)  Chromite-olivine  Rock.     This  is  like  dunite,  but  carries 
actinolite,  pearly  mica,  sporadic  diopside,  and   pyrrhotite. 


370  MANUAL    OF  LITHOLOG  Y. 

It  is  found  at  the  Eulengebirge  in  Silesia,  where  it  forms  a 
dark  green  lenticule,  thirty  feet  long,  in  amphibolite.  A 
serpentinized  variety  is  found  in  Steiermark,  and  in  Norway 
(in  quartzite  and  mica-schist)  is  a  similar  greenish  fine- 
grained aggregate  of  light  olivine,  colorless  pyroxene,  mica, 
and  chromite. 

OLIVINE-SCHIST. 

A  schistose  aggregate  of  predominant  olivine,  fresh  or 
serpentinized,  and  with  or  without  accessories.  Silica 
and  specific  gravity  as  above. 

This  occurs  to  a  slightly  less  extent  than  the  "  rock,"  as 
the  imposition  of  foliation  induces  changes  to  serpentine  or 
talc.  There  is  not  so  much  of  a  tendency  towards  predomi- 
nant minerals  associated  with  olivine  as  in  the  last  variety. 
As  accessories  are  smaragdite  in  prisms,  light  brown  en- 
statite,  chromite,  bronzite  prisms,  black  hornblende,  acicular 
tremolite,  augite,  gold,  garnet,  talc,  chlorite,  and  magnetite. 
It  is  found  in  Sweden,  Greenland,  Africa,  and  in  a  widely 
developed  zone  between  the  Blue  Ridge  and  the  Great 
Smoky  mountains  in  North  Carolina.  At  the  last  locality 
the  olivine  is  fresh  and  oil-green,  and  varies  from  a  distinct 
schist  to  a  rock  with  slight  foliation. 

EULYSITE  (Erdmann). 

A  thin-plated  aggregate  of  fayalite,  omphacite,  and 
brownish  red  garnet,  with  some  apatite  and  magnetite, 
and  (sporadically)  smaragdite-like  hornblende  and 
mispickel. 

This  occurs  near  Tunaberg,  Sweden,  in  a  thin  lenticular 
bed  in  granulite  (or  gneiss)  about  30  feet  thick  and  350  to 
500  feet  long. 


MINERALS  AS  ROCKS. 

Under  this  division  it  is  proposed  to  discuss  the  iron  ores, 
serpentine,  kaolin,  bauxite,  magnesite,  barite,  the  iron  sul- 
phurets,  and  sulphur.  Some  of  these  might  have  been  in- 
cluded under  the  previous  groups  if  their  origin  had  been 
a  single  one,  but  as  they  have  been  formed  in  a  number  of 
ways,  they  must  be  placed  by  themselves,  rather  than  split 
among  the  various  classes  according  to  the  forces  that  pro- 
duced each  portion.  The  others  are  simple  minerals  and 
only  of  local  occurrence,  so  that  their  bulk  is  inconsiderable 
in  comparison  with  the  simple  minerals  noted  in  the  previous 
pages.  They  will  be  described  without  further  discussion, 
and  those  of  similar  composition  will  be  grouped  together. 

THE    IRON    GROUP. 

LIMONITE  (Beudant,  not  of  Hausmann,  as  the  latter 
was  for  bog  ore  only),  Brown  Hematite  (Jameson), 
Brauneisenstein  (Ullman,  not  of  Werner  nor  Haus- 
mann, as  they  included  more  than  this  rock),  Bog- 
iron  ore  (Kirwan). 

A  compact,  earthy,  porous,  fibrous,  scaly,  oolitic  aggre- 
gate of  hydrated  sesquioxide  of  iron  ;  yellowish 
(through  brown)  to  black  ;  yellowish  brown  streak  ; 
with  accessory  manganese,  clay,  and  silica. 

Iron  59.89;  water  14.44;  H.  1-5.5  <  Gr.  3.4-3.95. 

It  occurs  at  the  bottom  of  marshes  (whence  the  name), 
ponds,  and  lakes,  where  it  has  settled  from  chemical  precipi- 

371 


3/2  MANUAL    OF  LITHOLOGY. 

tation  or  the  action  of  organisms  on  the  solutions  in  which 
it  is  held  ;  as  a  matrix  of  the  lower  layers  of  porous  strata 
resting  against  impervious  ones  ;  as  mixed  with  drift  when 
aggregated  from  old  surfaces  by  glacial  action  ;  as  replacing 
silica  in  chert  or  limestone  (dolomite)  in  beds  and  oolitic 
aggregations ;  as  alterations  of  hematite  or  siderite  ;  as  rust- 
ings  and  weatherings  of  ferruginous  minerals  (magnetite, 
pyritiferous  aggregates,  black  bisilicates,  etc.),  or  teachings 
from  ferruginous  soils  and  clays,  'it  is  thus  aggregated  with 
clay,  sand,  gravel,  and  other  impurities  in  more  or  less  com- 
pact forms.  It  forms  purer  concretions  of  varying  form 
from  shot  and  pea  sizes  to  aggregates  weighing  several  hun- 
dredweight. It  is  always  forming  and  quite  rapidly,  as  the 
clays  from  limonite  washings  that  have  been  emponded 
form  strata  of  considerable  depth,  which  have  along  their 
lower  layers  incipient  aggregations  of  a  soft  nature,  and  in 
several  cases  the  writer  has  found  shelly  concretions  about 
discarded  track-spikes  that  have  lain  in  moist  places — the 
spike  being  reduced  to  a  skeleton  of  the  impurities  in  the 
iron.  The  wooden  boxes  leading  water  from  coal  mines  in 
a  short  time  are  lined  with  a  layer  of  limonite,  and  whatever 
impurities  may  have  been  in  suspension,  as  a  compact  and 
hard  rock.  The  places  where  the  aggregations  take  place 
are  generally  hollows  in  the  surface  rocks,  or  in  beds  where 
replacement  is  in  progress.  In  some  cases  the  cavities  are 
caverns  hollowed  by  subterranean  solutions  whose  roofs 
have  fallen  in  or  been  removed  by  glacial  action.  It  is 
found  in  surface  hollows  mixed  with  clay,  drift,  etc.,  along 
the  Archaean  area  of  the  Atlantic  border  of  the  United 
States ;  as  cement  for  sands,  etc.,  in  Lehigh,  Northampton, 
Columbia,  and  (extensively)  Center  counties,  Pa.  ;  as  replac- 
ing silica  and  calcite  in  beds  from  Virginia  to  Georgia, 
Texas,  Vermont,  and  elsewhere.  These  can  be  divided 
into  two  general  varieties  : 


MINERALS  AS  ROCKS.  373 

(a)  Bedded,  where  the  aggregates  are  replacements  or 
concretions  in  definite  beds.     Here  the  impurities  are  those 
of  the  original  bed,  and  the  iron  is  more  generally  dissemi- 
nated through  the  mass  than  assembled  at  definite  points. 
Here  also  are  placed  the  fillings  of  veins,   cracks,  etc.,  in 
other  rocks. 

(b]  Loose,   where   the   ore    is   in   aggregates   distributed 
through  surface  accumulations,  and  can  be  readily  worked 
by  pick  and  shovel. 

As  far  as  general  appearance  of  the  individual  particles 
is  concerned,  there  is  little  difference  in  appearance  between 
these  two  divisions,  and  in  each  are  found  particles  from 
shot  sizes  up  to  many  feet  in  diameter  which  may  be  clayey, 
soft,  and  impure,  showing  the  lighter  colors  noted  above,  or 
comparatively  pure,  dark-colored,  and  hard.  The  shapes 
may  also  vary  from  massive  to  reniform,  stalactitic,  oolitic, 
scaly,  pisolitic,  concretionary  (solid  or  hollow), — in  the  last 
case  called  "  ore-pots," — or  the  ore  may  be  a  coloration  of 
clay,  sand,  etc.,  either  loose  or  hard  ;  if  the  former,  it  is 
yellow  ocher. 

RED  HEMATITE,  Specular  Iron. 

A  compact,  earthy,  fibrous,  scaly,  oolitic,  and  sometimes 
crystalline  aggregate  of  anhydrous  sesquioxide  of 
iron  ;  red  to  black  ;  streak  red  ;  with  accessory  man- 
ganese, silica,  and  clay ;  sometimes  magnetic,  and 
magnetipolar. 

Iron  70;  H.  2-6.5  ;  Gr.  4.5-5.2. 

This  occurs  like  limonite,  but  under  conditions  that 
favored  the  formation  of  anhydrous  sesquioxide,  such  as  the 
deposition  of  iron  oxide  in  heated  waters,  die  replacement 
of  silica  and  calcite  in  beds  in  hot  climates;  r*nd,  unlike  lim- 
onite, it  may  have  had  an  eruptive  origin  It  is  found  in 


374  MANUAL    OF  LITHOLOGY. 

beds  and  lenticular  masses  in  the  crystalline  schists,  and 
frequently  with  the  crystal  (specular)  form.  It  also  is  found 
as  original  or  replacement  formations  in  oolitic  aggregations, 
as  in  the  beds  of  the  Clinton  formation  from  New  York  to 
Alabama,  and  in  Wisconsin,  Illinois,  and  Kentucky.  In 
many  cases  this  is  a  replacement,  as  the  fragments  of  shells 
are  turned  to  ore,  and  in  the  interiors  of  many  of  the  un- 
changed ones  are  specular  crystals  from  the  intruding  solu- 
tions. The  extensive  beds  of  the  Penokee-Gogebic  region 
are  also  replacements ;  the  immense  beds  of  the  Marquette- 
Menominee  region  are  thought  by  some  to  be  eruptive,  and 
the  Mesabi  beds  to  be  precipitates  from  a  heated  ocean — as 
are  the  clay  ironstones,  which  are  mixtures  with  clay. 
There  are  decided  varieties  of  this  rock,  as  follows : 

(a)  Red  Hematite.     This  is  the  common  kind,  and  is  com- 
pact, earthy,  fibrous,  and  oolitic.     It  breaks  with  an  earthy 
to  silky  luster. 

(b)  Micaceous  Hematite.     This  is  a  variety  in  thin  folia. 
In  some  cases  it  is  interbedded  with  chlorite  schist,  as  in 
Hungary.      At  the  Republic  mine  in  Michigan  the  immense 
bed  is  formed  of  a  fine  micaceous  aggregate  with  metallic 
luster  and  somewhat  fissile  structure. 

(c)  Specular  Hematite.     This  occurs  in  crystalline  aggre- 
gates.    The  island  of  Elba  affords  fine  examples.     It  is  also 
found  at  Pilot  Knob,  Mo.,  in  the  Lake  Superior  region,  New 
York,  and  Canada. 

As  an  example  of  parallel  beds  of  varying  ores  the 
Lynchburg  region  of  Virginia  is  remarkable,  as  there  one 
/finds  limonite,  red  hematite,  and  magnetite  in  parallel  con- 
torted beds  between  chlorite-schists,  limestones,  and  sand- 
:stones.  When  the  inclosing  rocks  are  both  limestone,  the 
bed  is  limonite ;  when  limestone  on  one  side  and  sandstone 
oDr  schist  on  the  other,  red  hematite ;  when  sandstone  and 


MINERALS  AS  ROCKS.  375 

schist,  magnetite.     The  following  varieties  are  due  to  ad- 
mixtures with  other  minerals: 

(d]  Siliceous  Hematite.     This  is  a  replacement  of  silica 
by  hematite  to  form  a  jasper,  thence  a  jaspery  hematite, 
thence  a  hematite.    All  variations  can  be  found  in  the  many 
workings  of  Center  County,  Pa. 

(e)  Black  Hematite  is  a   manganiferous   variety   with  a 
black  color  and  streak. 

(/)  Menaccanite,  Ilmenite,  Titaniferous  Iron  Ore,  occurs 
in  beds  or  veins  in  diorite  at  Krageroe,  Norway,  and  in 
masses  at  Bay  St.  Paul,  Canada,  in  syenite.  It  also  occurs 
as  sands,  and  is  called  iserine. 

MAGNETITE. 

A  granular,  compact,  and  schistose  aggregate  of  a  com- 
pound of  protoxide  and  sesquioxide  of  iron  ;  black 
color  and  streak ;  metallic  luster ;  magnetic  and 
magnetipolar. 

Iron  72.41  ;  H.  5.5-6.5  ;  Gr.  4.9-5.2. 

This  occurs  in  beds  and  lenticular  masses  of  great  size  in 
gneiss,  mica-schist,  chlorite-schist,  hornblende-schist,  and 
granular  limestone,  and  is  found  in  the  Archaean  formations 
of  the  world,  and  especially  in  Scandinavia,  the  Urals,  east- 
ern North  America,  and  the  Lake  Superior  region.  Its 
origin  is  either  eruptive  or  metamorphic.  As  the  former  it 
occurs  in  gabbro  regions,  and  in  Rhode  Island  is  a  titan- 
iferous  magnetite  eruptive  (cumberlandite).  It  sometimes 
seems  to  be  a  metamorphosed  limonite  ;  in  north  Wales  it 
is  a  metamorphic  replacement  of  oolite.  Among  large 
masses  is  the  iron  mountain  of  Gellivara  in  Lulea-Lappmark 
which  is  over  500  feet  high,  i^  miles  wide,  and  3  miles 
long.  The  accessories  are  numerous,  as  would  become  a 
metamorphic  rock,  and  are  hematite,  chromite,  chlorite, 


t  MANUAL   OF  LITHOLOGY. 

titanite,  pyrite,  chalcopyrite,  quartz,   apatite,    hornblende, 
augite,  garnet,  feldspar,  etc.     The  varieties  are  : 

(a)  Catawbirite  (Lieber).     From  South  Carolina,  where  it 
occurs  in  great  abundance.     It  is  an  intimate  aggregate  of 
magnetite  and  talc. 

(b)  Chromic  Magnetite,  where  chromite  is  the  sole  acces- 
sory, and  is  predominant  in  the  mixture. 

(c)  Garnetiferous  Magnetite.      This   occurs   near   garnet 
rock,  and  passes  into  it. 

SIDERITE  (Haidinger),  Spathic  Iron. 

A  granular  to  compact  aggregate  of  carbonate  of  the 
protoxide  of  iron  ;  yellowish  white,  gray,  or  yellowish 
brown  ;   streak  white  ;   darkens  to  brown  or  black  on 
exposure  to  the  air ;  effervesces  with  acids. 
Iron  48.22;  H.  1-4.5;  G"r.  2.5-3.9. 

This  occurs  in  beds  and  masses  of  varying  dimensions, 
but  not  so  large  as  in  the  ores  already  described,  in  gneiss 
and  the  crystalline  schists,  and  as  beds  (with  clay)  in  recent 
formations  also ;  in  veins  in  the  oldest  rocks,  and  in  the  Erz- 
berg  in  Styria  forms  a  mountain  2700  feet  high.  As  black- 
band  and  clay  ironstone  it  occurs  in  beds  in  various  forma- 
tions. As  spathic  ore  it  is  found  at  Roxbury,  Conn. ;  as 
clay  ironstone,  in  the  Carbonic  of  the  Appalachian  area,  and 
as  a  bed  extending  under  Chesapeake  Bay.  As  black-band- 
it is  found  in  the  coal  measures  of  the  United  States  - 
though  not  worked,  owing  to  the  abundance  of  better  ores. 
As  varieties  are : 

(a)  Spharosiderite,  Clay  Ironstone,  is  a  dull  brown  to 
black  compact  form  of  siderite,  with  a  variable  mixture  of 
clay  and  some  organic  matter.  It  occurs  in  the  Carbonic 
and  other  formations  in  the  form  of  nodules  gathered  about 
some  object  (pebble,  leaf,  fossil),  or  as  beds  interstratified 
with  shales  and  coals. 


MINERALS  AS  ROCKS.  377 

(b)  Black-band.  A  compact  and  frequently  siliceous 
clay  ironstone  rendered  black  by  a  large  proportion  of  car- 
bon, and  with  so  much  of  it  that  it  will  inflame  in  heaps 
without  admixture  with  coal. 

FRANKLINITE  (Berthier). 

A  massive,  coarse-  to  fine-granular  and  compact  aggre- 
gate of  protoxides  of  iron,  zinc,  and  manganese,  com- 
pounded with  sesquioxides  of  iron  and  manganese; 
iron-black  ;  streak  dark  reddish  brown  ;  luster  metal- 
lic ;  acts  slightly  on  the  magnet. 

Iron   45-48;     zinc   9-20;    manganese   8-12;    H. 
5.5-6.5;  Gr.  5.07. 

This  may  be  called  a  manganese-zinc-magnetite.  It  oc- 
curs at  Franklin  and  Sterling  Hill,  N.  J.,  where  it  forms 
large  beds  in  granular  limestone,  and  is  associated  with 
massive  zincite  and  willemite.  This  is  its  only  occurrence 
as  a  rock. 

SERPENTINE  ("Ophites,"  Pliny). 

A  massive,  fine-granular  to  cryptocrystalline  and  com- 
pact rock,  sometimes  slaty,  soft,  with  greasy  feel ; 
dark  green  to  brown ;  usually  with  accessory  min- 
erals. 

Gr.  2.5-2.7;  H.  2.5-5.5. 

This  occurs  in  many  ways,  as  already  described  in  the 
foregoing  pages,  and  is  the  alteration  product  from  many 
minerals.  The  varieties  with  calcite  have  been  noted.  It 
frequently  is  porphyritic  from  phenocrysts  of  pyrope,  and 
often  slaty.  The  accessories  that  form  varieties  are  olivine, 
amphibole,  pyroxene,  garnet,  chlorite,  talc,  and  the  iron 
ores ;  less  frequently  quartz,  and  opal.  As  variations 
in  texture  and  structure  are:  (massive)  retinalite,  por- 
cellophite,  and  bowenite  ;  (lamellar)  antigorite,  from 


378  MANUAL   OF  LIT  HO  LOGY. 

Piedmont;  williamsite,  from  Texas,  Pa.;  (foliated)  mar- 
molite,  from  Hoboken,  N.  J.,  Blandford,  Mass. ;  ther- 
mophyllite,  from  Hopansuo,  Finland ;  (fibrous)  chrysotile, 
picrolite  —  both  abundant.  Admixture  with  opal  forms 
silicophite  (Schrauf) ;  with  garnet,  ^or^-serpentine ;  with 
bronzite,  bronzite-serpentine,  etc.  It  joints  irregularly  (ex- 
ceptionally it  is  columnar,  frequently  tabular).  It  is  most 
frequently  found  in  irregular  and  subordinate  beds  between 
crystalline  schists,  and  also  forms  the  necks  of  altered  erup- 
tives.  It  occurs  massive  and  in  workable  quantities  in  New 
England  and  along  the  Atlantic  States. 

BARITE,  Barytes,  Heavy  Spar. 

Sulphate  of  barium;  Gr.  4.3-4.7;  11.2.5-3.5;  white  to 
black  —  usually  white,  gray,  or  blue  (the  last  two 
being  transparent). 

It  occurs  as  a  gangue  in  metal-bearing  veins  throughout 
the  world,  and  in  veins  and  pockets  in  limestone.  It  is 
found  in  bowlders  and  nodules  in  clay  in  Virginia,  between 
slate  and  limestone,  and  in  surface  clay  in  Missouri.  The 
supply  in  the  United  States  comes  from  the  last  two  States, 
though  small  amounts  are  found  in  North  Carolina,  Illinois, 
and  New  England. 

MAGNESITE  (Brongniart). 

Carbonate  of  magnesia  ;  Gr.  3-3.2  ;  H.  3.5-4.5  ;  white  to 
brown  (according  to  the  amount  of  iron). 

It  occurs  associated  with  serpentine,  talc-schist,  and  other 
magnesian  rocks,  and  is  found  at  Veitsch  (Styria),  Austria; 
near  Frankenstein  (Silesia),  Prussia  ;  Mantoudi  (Euboea), 
Greece ;  and  Child's  Valley,  Cal.  The  Austrian  de- 
posits are  beds  conformable  to  Silurian  strata  ;  those  of 
Greece  are  in  large  veins  in  serpentine.  Magnesite  has  also 
been  reported  from  Bolton,  Canada. 


MINERALS  AS  ROCKS.  379 

KAOLIN,  Porcelain  Clay. 

Hydrous  silicate  of  alumina ;  Gr.  2.4-2.63  ;  H.  1-2.5  J 
white  when  pure,  but  colored  variously  by  impurities. 

This  occurs  as  the  alteration  by  weathering  of  aluminous 
minerals,  especially  feldspars  of  granite  and  gneissoid  rocks 
and  porphyries.  Where  weathering  has  taken  place  for  a 
long  time,  without  erosion,  there  remains  a  large  deposit  of 
kaolin.  It  is  found  in  the  Carbonic  measures  of  the  Appala- 
chian region,  and  forms  extensive  beds  in  the  Tertiary  for- 
mation near  Richmond,  Va.  A  variety  at  Lawrence  County, 
Ind.,  and  elsewhere  through  that  State,  with  a  great  amount 
of  water,  is  called  indianaite.  It  is  found  at  Brandon,  Vt. ; 
in  the  Cretaceous  and  Quaternary  of  New  Jersey ;  in  Del- 
aware, Maryland,  Missouri,  Oregon,  and  California. 

BAUXITE. 

Hydrated  sesquioxide  of  alumina  with  accessory  silica 
and  sesquioxide  of  iron;  Gr.  2.55;  H.  1-3;  whit- 
ish, yellowish,  brown,  red,  and  black,  and  always 
more  or  less  stained  with  iron,  manganese,  and  other 
minerals. 

This  occurs  as  sediments  (in  Europe)  alternating  with 
sandstones,  limestones,  and  clays ;  in  pockets  and  cavities  in 
limestone,  and  in  concretionary  grains  scattered  through 
the  limestones.  It  is  generally  oolitic  or  concretionary. 
The  geological  formations  where  it  is  found  are  Trias, 
Jurassic,  and  Miocene-Tertiary.  It  occurs  in  the  United 
States  in  residual  clays  and  irregular  and  ill-defined  de- 
posits, which  may  be  alteration  products  of  underlying  lime- 
stones, as  in  Europe.  The  geological  horizons  of  the  de- 
posits are  Lower  Silurian  and  Tertiary.  It  is  found  in 
Georgia,  Alabama,  Tennessee,  and  abundantly  in  Arkansas, 
where  it  is  said  to  be  inexhaustible.  It  is  a  source  of 
aluminium. 


MANUAL    OF  LITHOLO^ 

PYRITES. 

Sulphides  of  iron  of  varying  compositions;  Gr.  4.4-5.2; 
H.  3.5-6.5  ;  brass-yellow  ;  streak  grayish  black,  green- 
ish black.  Under  this  title  are  included  pyrite, 
pyrrhotite,  and  marcasite. 

These  occur  disseminated  in  small  quantities  through  the 
rocks  of  all  ages,  and  often  in  large  beds  of  such  size  as  to 
be  called  masses.  They  are  found  along  the  eastern  slope 
of  the  Appalachians  from  Maine  to  eastern  Alabama.  Mines 
have  been  worked  at  Capelton,  Canada,  Milan,  N.  H.,  Staf- 
ford, Vt,  Rowe,  Mass.,  and  Tolersville,  Louisa  County,  Va. 
The  'first  and  last  are  the  only  ones  at  date  affording  much 
of  an  output.  These  deposits,  though  large,  are  not  to  be 
compared  with  the  Rio  Tinto  deposits  that  stretch  from 
Spain  into  Portugal  in  two  vast  beds  or  veins  in  metamor- 
phic  schists.  The  southern  vein  is  300-400  feet  wide,  and 
at  least  2500  feet  long;  the  northern,  1300-1600  feet  wide, 
and  6000  feet  long.  At  Goslar  in  the  Harz  Mountains  is 
a  vein  ot  cupriferous  pyrites  which  is  350  by  1800  feet. 
At  Fahlun,  Sweden,  is  a  mass  of  similar  composition  in 
Archaean  gneiss  and  schists.  At  Agordo,  Tyrol,  is  a  mass 
in  talc-schist  and  clay-slate  varying  in  width  from  12  to  250 
feet.  Large  desits  also  occur  at  Domokos,  Transylvania, 
and  Schmollnitz,  Hungary. 

SULPHUR. 

Pure  sulphur;  Gr.  2.072 ;  H.  1.5-2.5;  color  and  streak 
sulphur-yellow. 

This  occurs  about  active  volcanoes  or  associated  with 
beds  of  gypsum.  We  can  therefore  divide  the  deposits  un* 
der  two  types : 

(a)  The  solfatara  type,  where  the  mineral  is  deposited 
directly  from  volcanic  exhalations  (H2S  and  SO2)  in  cracks 


MINERALS  AS  ROCKS.  38 1 

in  the  lava  and  tuffs,  or  in  the  clay  resulting  from  their  de- 
composition. 

(b)  The  gypsum  type,  where  bituminous  matter  acts  on 
gypsum  and  reduces  it  to  calcium  sulphide  and  water.  The 
former,  being  soluble,  is  affected  bythe  air,  while  in  solution, 
to  form  calcium  carbonate  and  polysulphide  of  calcium,  and 
the  latter  breaks  up  and  deposits  the  excess  of  sulphur. 

The  first  type  is  found  in  Italy,  Japan,  southern  Utah, 
and  is  extensively  worked  in  the-  two  last  —  the  first  being 
somewhat  exhausted.  The  second  type  is  found  associated 
with  gypsum  in  Sicily,  France,  Spain,  northeastern  Italy, 
Greece,  and  Poland  in  Miocene-Tertiary  formations.  Juras- 
sic beds  occur  in  the  Caucasus,  and  Quaternary  deposits  in 
southwestern  Louisiana. 


SCHEME  FOR  DETERMINING  THE  PRINCIPAL 

ROCKS. 

The  specimen  will  fall  under  one  of  the  four  grand  divi- 
sions, according  to  its  TEXTURE. 

(A)  Clastic,  fragmented,  or  sedimentary  (part),     p.  382. 

(B)  Compact,  dull,  or  subvitreous.     p.  384. 

(C)  Compact,  vitreous,  or  resinous,     p.  386. 

(D)  Crystalline-granular,     p.  387. 

It  will  then  be  tested  to  see  under  which  of  the  following 
heads  it  falls : 

I.  Untouched  or  slightly  touched  by  acids. 
II.  Partly  attacked  by  acids. 

III.  Completely  soluble  without  effervescence. 

IV.  Soluble  with  more  or  less  effervescence. 

V.  Burns  more  or  less  readily ;   detonates  with  KNO8. 

Having  determined  under  which  of  the  above  it  falls,  it 
will  then  be  examined  regarding  its  STRUCTURE,  whether  it 
be  (a)  Massive  ;  (b)  Stratified  or  schistose  ;  (c]  Porphyritic  ; 
(d)  Vesicular  or  amygdaloidal. 

Turning  to  the  following  pages,  a  list  of  rocks  will  be 
found  that  belong  to  each  group  indicated,  and  the  species 
can  be  determined  by  the  characteristics  there  given. 

(A)  CLASTIC   OR   FRAGMENTAL   ROCKS. 
I.    UNTOUCHED   BY  ACIDS. 

(a)  Massive  or  stratified. 

Infusible  and  insoluble  in  alkaline  solutions. 

Conglomerates  and  breccias  of  quartz,  jasper,  the  gran- 
ites, syenites,  etc. 

382 


SCHEME  FOR  DETERMINING    THE  PRINCIPAL  ROCKS.  383 

Sand,  gravel,  and  shingle. 
Sandstone,  grit,  and  arkose. 

Soluble  in  alkaline  solutions. 

Conglomerates  and  breccias  of  opal. 
Tripoli  and  tripoli-slate. 

Fusible. 

Conglomerates  and  breccias  of  felsite,  trachyte,  pitch- 
stone,  rhyolite,  the  mica-traps,  porphyrites,  etc. 

II.    PARTIALLY  ATTACKED   BY   ACIDS. 
(a)  Massive. 

Infusible  or  slightly  fusible. 

Clay  and  loam,  claystone,  shale,  clay-slate,  and  the  acid 
tuffs. 

Fusible  readily. 

Conglomerates  and  breccias  of  dolerite,  basalt,  phonolite, 
gabbro,  etc. 

The  various  basic  tuffs. 

III.   COMPLETELY   SOLUBLE  IN  ACIDS  WITHOUT  EFFER- 
VESCENCE. 

(a)  Massive  or  stratified. 
Give  water. 

Gypsum,  and  the  hydrated  iron  and  manganese  ores. 
Without  water. 

Anhydrite,  and  the  anhydrous  iron  and  manganese  ores, 
except  siderite. 

IV.    MORE   OR  LESS   SOLUBLE   IN  ACIDS  WITH   EFFERVES- 
CENCE. 

(a)  Massive  or  stratified. 

The  limestones  and  dolomites,  siderite,  marl,  travertine, 
and  tufa.  Conglomerates  and  breccias  of  the  above,  and 
bone-breccia. 


MANUAL    OF  LITHOLOGY. 

V.   BURN   MORE   OR  LESS   READILY. 
(a)  Massive  or  schistose. 
The  carbonic  and  hydrocarbonic  rocks. 


(£)  COMPACT;   DULL   OR   WITH    FEEBLE   LUSTER. 
I.   UNTOUCHED   BY  ACIDS. 

(a)  Massive. 

Infusible  ;  insoluble  in  potash  lye  ;  density  2.6. 

Chalcedony,  jasper,  Lydian  stone,  and  other  crypto- 
crystalline  varieties  of  quartz. 

Density  2.9  or  above. 

Euphotide,  the  variety  containing  Saussure's  jade  from 
Monte  Rosa. 

Soluble  in  potash  lye. 

Semi-opal,  siliceous  sinter,  and  other  cryptocrystalline 
forms  of  opal. 

Fusible. 

Compact  mass  and  hardness  6.     Felsite  ;  fine-grained  or 
microcrystalline    mass.      Leptinolite,  Adinole,  Porphyroid. 
The  compact  states  of  the  porphyrites. 

(b)  Stratified  or  schistose. 

Fusible. 

Porphyritic.  Slaty  Porphyry  ;  not  porphyritic.  Halle- 
flinta. 

Infusible. 

Novaculite. 

(c)  Porphyritic. 

With  quartz.  Quartz-porphyry  ;  with  quartz,  feldspar, 
and  mica.  Granite-porphyry  ;  without  quartz.  Feldspar, 
mica,  and  hornblende-porphyrite. 


SCHEME  FOR   DETERMINING    THE  PRINCIPAL   ROCKS.  385 

II.    PARTIALLY    ATTACKED    BY   ACIDS, 
(a)  Massive,  schistose,  porphyritic,  and  amygdaloidaL 

Infusible  or  slightly  fusible. 

Gray  mass  with  crystals  of  leucite  and  augite.  Leucite- 
phonolite,  and  compact  forms  of  leucite-bearing  rocks. 

Reddish  or  grayish  porous  mass,  with  bluish  crystals  of 
haiiyne.  Haiiynophyre. 

Easily  fusible. 

Color  green  rather  than  black,  decolorized  by  HCL 
Augite  porphyrite,  Aphanite. 

Mass  like  the  above  with  grains,  globules,  or  pustules  of 
a  hardness  of  6,  fusible.  Variolite. 

Bluish  or  grayish  black  mass,  usually  with  olivine,  sel- 
dom containing  quartz,  more  commonly  calcite  or  zeolites, 
in  amygdaloidal  cavities,  fuses  to  black  globule,  density 
generally  3.  Basalt. 

Compact  mass,  black  on  fresh  fracture,  weathers  reddish, 
fusible  to  bottle-green  globule,  never  with  olivine,  fre- 
quently with  quartz  in  amygdaloids,  density  generally  less 
than  3.  Melaphyre. 

Compact,  subgreasy  mass,  smooth  fracture,  gray  color, 
density  2.6,  easily  fusible.  Nepheline-basalt. 

Compact,  dull,  greenish  mass,  fusible  to  white  globule, 
yields  water  when  heated,  gelatinizes  in  HC1,  with  sanidine 
in  crystals.  Phonolite. 

III.    COMPLETELY   SOLUBLE  WITHOUT  EFFERVESCENCE. 

(a)  Massive,  stratified,  and  sometimes  porphyritic. 
Give  water. 

Hardness  1.5-2,  give  sulphur  and  lime.     Gypsum. 

Hardness  3-4,  rarely  5,  green,  red,  brown,  sometimes  is 
porphyritic  from  crystals  of  garnet,  blackens  before  the 
blowpipe  and  fuses  with  difficulty.  Serpentine. 


386  MANUAL   OF  LITHOLOGY. 

Give  iron  or  manganese  reaction,  density  3.5-4.5.  Hy- 
drous ores  of  iron  and  manganese. 

Give  no  water. 

Give  sulphur  and  lime.     Anhydrite. 

Give  iron  or  manganese  reaction,  density  4.5-5.5.  An- 
hydrous ores  of  iron  or  manganese. 

IV.    MORE   OR  LESS   SOLUBLE  WITH   EFFERVESCENCE. 

(a)  Massive  and  stratified. 

Hardness  under  3,  infusible. 

Some  limestones,  dolomites,  and  calcareous  clay  slates. 
A  mixture  of  calcite  and  serpentine.     Ophiolite. 

(C)  COMPACT,  VITREOUS,  OR   RESINOUS. 
I.   UNTOUCHED   OR  SLIGHTLY   TOUCHED   BY  ACIDS. 

(a)  Massive,  schistose,  and  sometimes  porphyritic. 
Infusible,  soluble  in  potash  lye,  never  porphyritic.    Opal, 

Siliceous  Sinter. 

Fusible. 

Conchoidal  fracture,  fusible  to  a  blebby  globule.  Ob- 
sidian. 

Pearly  luster,  splintery  fracture,  gives  water  in  the  open 
tube,  frequently  containing  round  grains.  Perlite. 

Resinous  luster,  conchoidal  fracture,  fuses  without  in- 
tumescence to  a  white  vesicular  glass.  Pitchstone ;  with 
balls  of  felsite,  or  crystals  or  grains  of  feldspar,  and  quartz. 
Pitchstone-porphyry. 

Mass  porous,  perlitic,  sometimes  slaty,  with  crystals  of 
sanidine,  mica,  or  quartz.  Rhyolite. 

(b)  Vesicular,  scoriaceous,  pumiceous. 

Perlite  and  obsidian  occur  in  the  first  two  states ;  when 
in  the  third,  the  rock  is  called  pumice.  Dark  mass,  fusible 


SCHEME  FOR  DETERMINING    THE  PRINCIPAL  ROCKS.  387 

to  black  slaggy  globule,  heavier  than  pitchstone,  obsidian, 
or  perlite.     Hyalomelane. 


II.   DECOMPOSED  BY  ACIDS. 

(a)  Massive  and  vesicular. 

Dark  mass,  fusible  to  black  slaggy  globule,  heavier  than 
pitchstone,  obsidian  or  perlite.  Tachylite. 

(JD)    CRYSTALLINE   OR   CRYSTALLINE-GRANULAR. 
I.    UNTOUCHED   OR   SLIGHTLY  TOUCHED   BY  ACIDS. 

(a)  Massive,  and  frequently  porphyritic. 

Coarse  crystalline-granular  or  granitoid. 

Quartz,  orthoclase,  and  granite,  with  mica  replaced  by 
talc  or  chlorite.  Protogine ;  by  tourmaline.  Tourmaline- 
granite  ;  with  tourmaline  abundant  and  flesh-red  orthoclase. 
Luxullian  ;  mica  replaced  by  epidote.  Epidote-granite ;  by 
iolite.  Cordierite-granite ;  by  hornblende.  Syenitic  Gran- 
ite. 

With  the  quartz  arranged  in  layers  on  the  cleavage 
planes  of  the  orthoclase  and  white  mica.  Graphic  Granite. 

Like  the  last,  but  more  coarse  and  irregular.    Pegmatite. 

Quartz  and  orthoclase.     Aplite. 

Quartz  and  zinnwaldite.     Greisen. 

Orthoclase  and  hornblende.     Syenite. 

Oligoclase  and  hornblende,  greenish  appearance.  Diorite. 

Oligoclase,  hornblende,  and  quartz.     Quartz-diorite. 

Oligoclase,  hornblende,  quartz,  and  biotite,  fusible. 
Tonalite. 

Oligoclase,  orthoclase,  hornblende,  mica,  and  quartz. 
Mica-diorite. 

Cyanite  and  white  mica,  with  garnets,  infusible.  Cyanite 
Rock. 


MANUAL    OF  LITHOLOGY. 

Mica,  garnet,  and  iolite.     Kinzigite. 
Garnet  and  smaragdite.     Eclogite. 

Fine  crystalline -granular. 

Rough  mass,  containing  crystals  of  sanidine  and  horn- 
blende, density  2.6,  mass  fusible  to  coLorless  glass  or  enamel. 
The  Trachyte  group. 

Grayish  mass,  containing  much  magnesian  mica  in 
laminae,  infusible  or  slightly  fusible.  Minette. 

Fusible  mass,  with  much  magnesian  mica  in  laminae  and 
crystals  of  hornblende,  and  oligoclase.  Kersantite. 

Reddish  mass,  hardness  7,  attacked  by  HCi  after  long 
heating,  density  3.4-4.3.  Garnet  Rock. 

Diallage  and  Saussure's  jade  (compact  zoisite)  fusible 
\vith  difficulty,  gelatinizes  after  fusion.  Euphotide  (in  part). 

Rough  porous  mass,  gray  or  black,  with  crystals  of  oligo- 
clase and  hornblende.  Andesite. 

Like  the  above,  but  pyroxene  replacing  the  hornblende. 
Pyroxene-andesite. 

Grayish,  porous,  crumbly  mass  like  claystone,  oligoclase, 
hornblende  or  augite,  and  dark  mica.  .  (Domite  from  the 
Puy  de  Dome) ;  same  composition,  undecomposed.  Domite. 

(b)  Stratified  or  schistose  and  frequently  porphyritic. 

Contain  feldspar. 

Orthoclase  or  oligoclase,  quartz  and  mica.  Gneiss ;  with 
talc  or  chlorite  replacing  mica.  Protogine-gneiss  ;  with 
iolite  for  mica.  Dichroite-gneiss ;  with  hornblende  for 
mica.  Syenitic  Gneiss. 

Plagioclase  and  hornblende.  Diorite-gneiss,  Gabbro- 
gneiss. 

Orthoclase  and  black  mica,  grayish  or  brownish  mass. 
Schistose  Minette. 

Orthoclase  and  quartz,  frequently  with  garnet  and  cya- 
nite.  Granulite. 


SCHEME  FOR   DETERMINING    THE  PRINCIPAL   ROCKS.  389 

Without  feldspar  and  with  quartz. 

Quartz  in  crystalline  grains.     Quartzite,  Quartz-schist. 

Quartz  and  a  little  white  mica,  in  thin  sheets,  flexible. 
Itacolumite. 

Quartz  and  much  mica.     Mica-schist. 

Quartz  and  tourmaline.     Tourmaline-schist. 

Quartz,  tourmaline,  and  topaz.     Topaz  Rock. 

Quartz,  in  greater  or  less  amount,  and  talc.  Talc-schist ; 
with  pyrophyllite  in  place  of  talc,  and  no  quartz.  Pyroph- 
yllite-schist. 

Quartz  and .  hornblende,  sometimes  hornblende  alone, 
fusible  to  black  or  dark  green  enamel.  Hornblende-schist; 
an  aggregate  of  actinolite.  Actinolite-schist ;  with  glauco- 
phane,  Glaucophane-schist ;  with  epidote  and  glaucophane, 
either  Epidote-glaucophane-schist  or  the  reverse,  dependent 
on  which  is  predominant. 

With  much  argillaceous  matter,  Argillite  ;  with  much 
argillaceous  matter  and  much  mica,  quite  easily  fusible, 
Phyllite ;  with  ottrelite,  Ottrelite-schist ;  with  chiastolite, 
Chiastolite-schist ;  with  decomposed  pyrite,  Alum-schist; 
with  carbonaceous  matter,  Black  Chalk. 

(c)    Vesicular  and  amygdaloidal. 

Feldspathic  mass,  density  2.6,  rough,  and  generally  more 
or  less  fusible.  Vesicular  Rhyolites  and  Trachytes. 

II.    PARTIALLY  ATTACKED   BY   ACIDS. 

(a)  Massive. 

Pyroxene,  white  or  gray  labradorite,  or  oligoclase,  and 
magnetite,  sp.  gr.  2.9-3,  color  generally  black  or  gray. 
When  coarse-crystalline,  Dolerite ;  when  fine-crystalline, 
Anamesite. 

Augite,  labradorite,  or  oligoclase,  viridite,  and  magnetite, 
color  greenish.  Diabase. 


39°  MANUAL    OF  LITHOLOGY. 

Pyroxene  and  nepheline,  greasy  luster,  sp.  gr.  2.6.  Neph- 
eline-dolerite. 

Pyroxene  and  leucite,  the  latter  in  rounded,  indistinct 
crystals.  Leucite-dolerite. 

Pyroxene  and  hauyne  with  olivine,  mica,  and  leucite ; 
porous  ;  brownish  or  grayish  color.  Hauynophyre. 

Pyroxene  and  hornblende  with  labradorite  and  oligo- 
clase,  frequently  some  mica ;  gray  or  brown ;  mass  fine- 
crystalline  to  compact.  Trachydolerite. 

Diallage  and  plagioclase ;  easily  fusible ;  pearly  luster. 
Gabbro. 

Diallage,  plagioclase,  and  much  dark  olivine.  Olivine- 
gabbro. 

Plagioclase  and  hypersthene,  or  bronzite.     Norite. 

Hornblende,  labradorite,  and  oligoclase.     Labradiorite. 

Orthoclase,  elaeolite,  zircon,  and  hornblende.  Elaeolite- 
syenite. 

Orthoclase,  red  elaeolite,  and  hornblende.     Foyaite. 

Greenish  black  hornblende  and  anorthite.  Anorthite- 
diorite ;  if  arranged  in  concentric  crystalline  rings,  alter- 
nating with  one  another.  Orbicular  Diorite. 

Deep  green  hornblende,  white  or  gray  anorthite,  and 
little  quartz.  Egeran. 

Hypersthene  in  long  black  needles,  augite,  and  labrador- 
ite. Teschinite. 

Pyroxene  and  anorthite.     Eukrite. 

Yellow  or  green  chrysolite  (decomp.  by  H,SO4 ;  sol.  in 
HC1  and  chromite).  Dunite. 

Fine-grained,  greenish  gray  mass  with  vitreous  feldspar 
(sanidine);  weathers  with  a  sharply  denned  white  crust. 
Phonolite. 

(b)  Stratified  or  schistose. 

Fine-grained,  greenish  gray  mass,  showing  cleavage  sur- 


SCHEME  FOR   DETERMINING    THE  PRINCIPAL   ROCKS.   3QI 

faces  of  a  vitreous  feldspar ;  weathers  with  sharply  defined 
white  crust.  Phonolite. 

Pyroxene,  labradorite,  viridite ;  color  greenish.  Diabase- 
schist. 

Fine-grained,  greenish,  hardness  2.5-4.     Chlorite-schist. 

(c)  Porphyritic. 

States  of  the  rocks  described  under  (a)  and  ^b). 

(d)  Vesicular  and  amygdaloidal. 

The  dolerite  group,  Diabase,  Phonolite. 
Cavities  filled  with  analcite.     Analcimite. 

III.    COMPLETELY  SOLUBLE  WITHOUT  EFFERVESCENCE. 

(a)  Massive. 

The  iron  and  manganese  ores. 

White,  hardness  2.5  ;  completely  soluble  in  HaSO4,  giving 
HF.  Cryolite. 

IV.   MORE  OR  LESS  SOLUBLE  WITH   EFFERVESCENCE. 

(a)  Massive. 

The  limestones  and  dolomites,  siderite,  and  travertine. 
Greenish  felsitic  mass  with  much  mica ;  iron  pyrites  fre- 
quently.    Fraidronite. 

(b)  Stratified  or  schistose. 

Quartz,  mica,  and  more  or  less  calcite.  Calcareous  Mica- 
schist. 

Calcite  and  mica.     Cipolino. 

Greenish  mass,  hardness  5 ;  contains  calcite.  Kalk- 
aphanite. 


THE  ECONOMIC  VALUE  OF  ROCKS. 

In  the  previous  pages  the  different  rocks  of  the  earth's 
crust  have  been  described  and  their  accessories  given.  The 
latter  are  sometimes  beneficial  and  sometimes  injurious 
when  we  examine  the  variety  from  the  standpoint  of  value, 
and  that  is  the  reason  why  long  lists  of  accessory  minerals 
have  been  noted,  when  they  made  no  variation  in  species, 
and  exerted  no  influence  upon  the  color  or  general  charac- 
ter. It  remains  to  briefly  examine  the  rocks  from  another 
standpoint  and  to  see  how  they  are  useful.  In  this  light  the 
majority  of  them  are  found  to  be  interesting  from  their 
differences,  but  are  either  inconsiderable  in  quantity,  or 
worthless  from  structural  or  other  defects.  The  useful  rocks 
that  remain  are  few,  and  in  such  quantity  that  it  will  pay  to 
assemble  the  necessary  machinery  to  work  them. 

The  general  value  of  a  deposit  depends  on  its  amount, 
the  shape  in  which  it  is  presented,  and  its  distance  from 
market.  The  last  generally  disappears  with  the  advent  of 
civilization,  and  the  market  comes  to  the  deposit  if  it  be 
valuable,  as  the  greater  portion  of  the  forces  tending  to 
civilize  the  race  had  their  impetus  from  a  desire  to  secure 
lasting  temples  for  their  divinities,  and  to  fitly  adorn  them, 
so  that  traffic  in  stones  required  roads,  and  the  growth  of 
taste  inspired  arts  of  adornment.  We  can  describe  the 
savage  as  the  man  of  the  stone  age,  where  the  spallings  of 
nature  were  utilized,  and  the  civilized  man  as  the  man  of 
metals.  The  second  of  the  above  conditions  is  always  an 
important  one,  for  upon  k  depends  the  sizes  of  the  pieces 

392 


THE  ECONOMIC   VALUE  OP  ROCKS.  393 

obtained  and  their  shapes.  A  bed  ol  first-class  granite  may 
be  so  jointed  and  fissured  that  it  cannot  be  gotten  out  in 
pieces  of  any  size,  and  can  only  furnish  smaller  material, 
like  Belgian  blocks  for  paving.  In  the  same  way  the  acces- 
sory minerals  affect  the  value  of  mortars,  abrasives,  ferti- 
lizers, lubricants,  etc.,  and  injurious  ones  that  cannot  readily 
be  removed  destroy  them  entirely ;  so  that  the  examination 
of  a  deposit  should  not  end  with  a  survey  that  determines 
its  bulk,  but  should  include  an  analysis  of  its  surface  im- 
purities and  a  study  of  the  same  at  depths,  as  weathering 
may  have  removed  harmful  portions;  and  should  further 
determine  the  purposes  for  which  it  is  unfit,  as  well  as  those 
to  which  it  is  adapted. 

As  the  principal  use  of  rocks  is  as  materials  for  construc- 
tion, those  fit  for  such  a  purpose  will  first  be  considered. 
They  may  be  utilized  as  spallings,  or  in  bulk  ("  dimension 
stones  ").  Their  value  in  the  latter  case  depends  upon  their 
strength  and  life,  and  these  vary  with  the  means  ot  con- 
solidation, which  are : 

1.  Intercrystallization  of  the  minerals  together  without 
cementing  material. 

2.  Compression  of  the  clastic  grains  so  that  they  have 
been  forced  to  fill  the  inequalities  in  those  adjacent,  and 
thus  approach  the  intercrystallization  of  the  first  case. 

3.  A  cementing  medium,  which  may  be : 
(a)  Silica. 

(£)  Clay. 

(c)  Calcite. 

(d)  Iron  oxides. 

The  strength  of  a  rock  depends  on  its  compactness,  free- 
dom from  a  cementing  medium,  hardness,  and  position  with 
respect  to  its  bedding  planes ;  so  that  rocks  formed  through 
the  first  two  means  are  stronger  than  those  formed  through 
the  third — if  of  equal  hardness  and  compactness. 


394  MANUAL    OF  LITHOLOGY. 

The  hje  of  a  rock  varies  with  the  resistance  to  weather- 
ing of  its  weakest  part,  so  that  uniformity  of  composition  is 
a  prime  requisite.  Conditions  that  favor  weathering  are : 
possessing  cements  of  clay,  calcite,  and  iron  oxides ;  ad- 
mixtures with  pyritous  minerals,  or  whatever  will  readily 
seek  more  stable  forms.  In  fine,  the  aggregates  of  the  most 
stable  minerals  will  live  longer  that  unstable  ones.  The 
locality  in  which  the  rock  is  to  be  used  must  be  considered, 
as  this  greatly  influences  the  rock  value.  A  porous  rock 
that  would  readily  scale  with  frost  in  the  latitude  of  New 
York  City  would  weather  well  in  Florida  and  more  tropical 
regions.  Evenness  of  temperature  is  a  prime  factor  in  lon- 
gevity, and  a  stone  that  would  spall  under  the  changes  of 
temperature  at  New  York  would  last  well  in  the  even  tem- 
perature of  the  Pacific  coast  from  California  to  Washington. 
This  is  the  reason  why  Egyptian  monuments  have  retained 
their  freshness,  though  exposed  to  fierce  heats ;  but  have 
scaled  through  the  variations  in  temperature  when  removed 
to  this  and  other  climates.  Porosity  does  not  enter  here,  as 
so  dense  a  rock  as  the  Potsdam  quartzite  in  a  few  years 
takes  spheroidal  shapes  through  changes  in  temperature, 
while  the  rock  is  fresh,  as  shown  in  recent  railroad  cuts. 
We  must  therefore  consider  the  region  in  which  the  rocks 
are  to  be  used,  and  the  effects  of  variation  in  temperature, 
as  well  as  changes  in  atmospheric  conditions.  Under  the 
latter  comes  the  difference  in  behavior  of  the  magnesian 
limestone  of  which  the  houses  of  parliament  of  Great  Britain 
are  built.  When  used  to  build  country  seats,  it  has  lasted 
for  years  in  pure  air,  but  the  gas-laden  air  of  London  is 
surely  destroying  it.  The  economic  value  of  a  rock,  there- 
fore, depends  on  many  conditions  outside  of  its  composition. 
The  different  rocks  fit  for  constructive  purposes  will  now  be 
discussed. 

Granite.     Under  this  head  will  be  noted  the  primary 


THE  ECONOMIC    VALUE   OF  ROCKS.  395 

rocks  and  similar  crystalline  schists.  The  most  durable  are 
'those  with  fine  grain,  with  small  amounts  of  the  black  bisili- 
cates,  not  too  much  feldspar,  and  compact  and  non-porous 
structure.  The  admixture  with  too  many  accessories  allows 
too  much  variation  in  expansion  among  the  ingredients,  and 
-consequent  strain  in  the  mass ;  or,  with  pyritous  minerals, 
carries  weathering  to  its  interior ;  while  porous  feldspathic 
varieties  absorb  moisture  and  readily  kaolinize.  The  beauty 
of  a  granite  is  in  its  uniformity  of  grain  and  color ;  so  that 
variations  in  the  first,  and  inclusions  of  foreign  rocks  (more 
or  less  resolved),  such  as  knots  of  mica-schist,  etc.,  lower  the 
value.  Gneiss  is  often  as  good  as  granite,  and  generally 
does  not  absorb  as  much  heat,  so  that  it  cannot  be  subjected 
to  as  sudden  strains  by  changes  in  temperature,  but  it  is 
never  as  uniform  in  color.  Diabase  and  diorite  cannot  be 
compared  with  the  above,  as  they  readily  weather;  and 
basalt  is  inferior  from  the  same  cause,  as  well  as  from  its 
being  fine-jointed,  so  that  it  cannot  be  obtained  in  large 
pieces,  and  its  brittleness  forbids  its  ready  dressing.  For 
want  of  a  better  stone  trachyte  is  sometimes  used ;  but  in 
competition  with  granite  (under  which  syenite  is  included) 
.and  gneiss  the  porous  extrusives  are  of  little  value  in  cli- 
mates with  severe  frosts,  but  can  be  used  in  the  tropics. 
The  exceptions  to  this  statement  are  the  phonolites  which 
have  been  rendered  slaty,  and  the  devitrified  basalts  and 
rhyolites  which  have  been  altered  and  transformed  to  slates, 
but  these  are  not  used  in  masses,  so  that  the  above  rule 
holds  good. 

Sandstone.  The  nearer  this  rock  comes  to  the  second 
condition  above  given,  and  is  free  from  cementing  media, 
the  better  it  is  for  building  purposes.  A  small  amount  of 
clay  will  not  lower  the  strength  of  a  fine-grained  variety  ; 
but  if  coarse-grained  and  porous  it  will  absorb  water  and 
cause  the  rock  to  swell.  Some  rather  fine-porous  stones 


396  MANUAL   OF  LITffOLOGY. 

will  be  unfit  for  immediate  use  if  quarried  at  or  near  water 
level,  as  they  will  be  full  of  moisture.  This  will  make  a. 
damp  wall  on  the  inside,  and  flake  under  frost  on  the  out- 
side ;  so  that  the  stone  should  be  well  seasoned  before  being- 
dressed  and  used.  Calcareous  cements  in  sandstone  will 
invariably  and  speedily  dissolve  and  allow  the  rock  to- 
crumble.  The  best  varieties  are  those  purely  siliceous,  of 
fine  grain,  and  free  from  pores,  cements,  and  unstable  acces- 
sories. 

Limestone*  This  is  generally  not  as  fit  for  exteriors  as 
sandstone,  as  it  weathers  more  readily,  and,  as  it  is  not  as 
stable  a  compound,  the  accessories  form  new  combinations 
with  it  to  its  disadvantage.  Limestones  should  be  as  free 
as  possible  from  all  cements,  excepting  silica.  Ferruginous 
cements  are  worse  here  than  in  sandstone,  as  they  react  on 
the  stone,  and  carry  to  the  interior  the  process  of  disintegra- 
tion. Pyritous  aggregates  have  the  same  effect.  Coarse- 
crystalline  silica  unfits  the  stone  for  careful  working,  but 
fine-crystalline  silica  adds  to  its  strength.  The  weathered 
outcrops  will  allow  us  to  determine  the  result  of  time  upon 
a  given  stone.  The  beauty  of  a  stone  is  frequently  destroyed 
by  such  an  accessory  as  the  mineral  oil  in  the  Niagara  lime- 
stone in  northern  Illinois.  When  quarried,  it  is  white,  but 
soon  becomes  smutty  in  cities,  while  it  remains  cleaner  in 
the  purer  air  of  the  country.  As  the  oil  is  not  evenly  dis- 
tributed, the  stainings  are  irregular,  and  are  thought  some- 
times to  add  to  the  appearance  of  the  stone. 

Marble.  In  the  language  of  the  trade  any  stone  that  is 
fine-grained  and  capable  of  taking  a  polish  is  a  "  marble,"  so 
that  many  ordinary  limestones  fall  under  this  designation. 
The  true  marbles,  will  however,  occupy  the  greater  part  of 
the  material  sold  under  the  name.  For  exteriors  dense  and 
strong  stones  are  necessary,  while  loose  and  soft  ones  can  be 
used  inside.  In  any  case  the  stone  should  not  be  placed 


THE  ECONOMIC   VALUE    OF  ROCKS. 

•where  it  will  be  subjected  to  strain,  or  it  will  crack,  if  not 
crush.  The  modern  methods  of  sawing  stone  from  the  solid 
in  the  quarry  and  working  the  product  with  the  sand-blast 
allow  us  to  market  many  brittle  stones  that  formerly  could 
not  be  used. 

Slate.  Not  all  parts  of  slate  deposits  are  valuable. 
.Slates  should  split  readily  and  into  thin  and  even  plates. 
All  seams  and  streaks  of  quartz,  calcite,  and  other  acces- 
sories should  be  avoided,  as  they  condemn  the  product. 
Contaminations  of  pyrites,  too  much  calcite  as  a  cementing 
medium,  and  too  great  porosity  shorten  the  life  of  slate. 
Weathering  takes  place  mechanically  and  chemically.  The 
mechanical  part  is  like  the  straining  already  noted  from 
changes  in  temperature,  and  slates  are  more  subject  to  this 
than  other  stones,  owing  to  their  color  and  exposure  to 
greater  amounts  of  heat.  They  are  further  unfortunate  in 
being  placed  with  the  bedding  exposed  to  the  weather,  so 
that  the  strain  comes  along  those  planes  where  cleavage  is 
readiest,  and  the  changes  from  day  to  night,  or  from  sun 
to  shower,  induce  great  and  sudden  strains.  The  chem-' 
ical  weathering  is  on  a  parallel  with  that  in  limestones, 
and  is  due  to  the  decompositions  of  the  accessories  and  the 
attempt  to  form  stable  compounds  at  the  expense  of  the 
rock.  Both  forms  of  weathering  are  going  on  at  the  same 
time,  so  that  in  the  purest  slates  mechanical  weathering 
loosens  the  outer  film  in  minute  folia,  and  these  are  knocked 
off  by  the  impact  of  rain-drops.  The  slates  free  from  im- 
purities and  exposed  in  the  purest  air  will  weather  rapidly, 
but  the  color  of  the  roof  will  show  whether  the  weathering 
is  mechanical  or  chemical.  Good  slate  will  show  dark  after 
3Tears  of  exposure,  but  bleached  and  mottled  slate  shows 
-chemical  action  on  too  great  an  amount  of  cementing  me- 
dium, or  on  spots  of  impurities.  Those  wishing  to  study 
the  strength  of  slates  will  find  Dr.  Merriman's  discussions 


398  MANUAL    OF  LITHOLOGY. 

before  the  American  Society  of  Civil  Engineers  of  great 
value. 

Clays.  For  brick  and  coarse  constructions  all  clays  are 
more  or  less  useful,  but  it  may  be  well  to  bear  in  mind  that 
alkalies  make  clay  fusible ;  and  while  a  small  amount  may  be 
good,  and  may  render  the  product  denser,  too  much  will 
make  it  so  fusible  that  it  will  warp  during  firing,  or  en- 
danger the  strength  of  a  structure  during  a  conflagration, 
where  only  a  part  is  on  fire.  Pottery  clays  are  mixtures 
of  kaolin,  as  the  pure  mineral  shrinks,  cracks,  and  checks,  so 
as  to  spoil  the  product.  Silica  counteracts  this.  Iron  is  the 
most  undesirable  accessory  under  any  form,  as  it  destroys 
the  white  color.  Fire-clays  are  found  as  the  under-clays  of 
the  coal-beds,  where  vegetation  has  removed  the  alkalies 
and  alkaline  earths.  Any  accessories  that  tend  to  flux  the 
clay  must  be  looked  for  in  the  examination  of  the  deposit 
for  this  purpose.  Segregations  of  "  giant  granite "  are 
valuable  for  the  feldspar,  which  is  ground  and  used  as  a  flux 
or  admixture  in  the  paste.  Flints  are  used  after  grinding 
"for  similar  mixtures. 

Sands.  These  are  used  for  glass  of  varying  kinds. 
Clean  sea  sand  free  from  iron,  or  sands  from  the  modified 
drift  of  the  northern  part  of  the  United  States,  as  well  as 
some  weathered  outcrops  of  the  calciferous  sand-rock,  are 
valuable  for  making  ordinary  window-glass,  but  flints  are 
necessary  for  the  whiter  and  clearer  article.  For  bottles 
(green)  any  sand  will  do,  and  even  granulite  is  used  in 
abundance,  as  it  contains  the  necessary  ingredients,  and  can 
be  charged  at  once  into  the  furnace.  It  is  found  in  Canada 
and  the  eastern  part  of  the  United  States.  Sands  for  mold- 
ings must  have  sufficient  clay  to  keep  the  form. 

Mortar,  Cement.  Limestone  for  mortar  should  not 
have  more  than  8  per  cent  of  silica  or  similar  impurities  if 
first-class  mortar  is  desired.  Hvdraulic  cements  are  found 


THE   ECONOMIC   VALUE   OF  ROCKS.  399 

along  the  junctions  of  slates  and  limestones,  but  all  such 
junctions  are  not  "  hydraulic."  Those  that  "  set "  under 
water  are  called  "  cements "  when  they  set  without  first 
slaking-,  but  "  hydraulic  limes "  when  they  slake  first. 
Specimens  should  be  burned  and  ground  to  see  whether 
this  property  is  inherent,  as  without  it  the  deposit  is  neither 
limestone  nor  slate,  and  of  little  value. 

Abrasives.  For  grinding  and  polishing  it  is  necessary 
to  secure  something  harder  than  the  body  to  be  treated. 
It  is  not  always  necessary  to  secure  the  hardest  substance. 
We  can  divide  the  abrasives  into  the  hard,  medium,  and 
soft  varieties.  The  hard  comprise  the  corundums,  which 
are  found  in  the  Archaean  formations,  and  are  separated 
from  the  matrix  by  grinding,  and  removing  the  iron  ores 
with  the  magnet.  The  medium  abrasives  are  ordinary  sand 
(quartz),  garnet,  and  other  minerals  of  similar  hardness  that 
are  found  in  sufficient  abundance.  The  soft  abrasives  are 
tripoli  and  infusorial  earth.  Tripoli  is  also  used  as  the  dope 
in  dynamite.  As  compact  abrasives  the  novaculites  of  Ar- 
kansas are  predominant  in  this  country,  though  gritty  mica- 
schists  and  metamorphic  phyllite  are  used  for  coarse  hones. 
The  best  and  finest  oil-stone  in  the  world  is  the  microcrystal- 
line  garnet  rock  of  Belgium.  For  millstones  gritty  sand- 
stones, buhrstones,  porous  porphyries,  etc.,  are  used. 

Lubricants.  The  minerals  used  for  diminishing  friction 
are  graphite,  talc,  and  mica.  All  of  them  must  be  free  from 
grit.  It  has  been  found  that  their  value  lies  in  the  fact  that 
they  are  foliated,  and  the  best  graphite  lubricant  is  now 
delivered  in  flakes  rather  than  in  powder.  Mica  is  freed 
from  grit  and  ground  to  a  flaky  impalpable  sand.  In  this 
way  the  micaceous  segregations  in  "  giant  granites  "  can  be 
utilized.  In  the  same  way  the  foliated  varieties  of  talc  and 
graphite  are  generally  freer  from  impurities  than  the  crystal- 


400  MANUAL   OF  LITHOLOGY, 

line  states,  and  are  more  readily  and  better  adapted  to  the 
market. 

Fertilizers.  For  this  the  phosphorites  and  guano  fur- 
nish phosphorus,  and  peat  improves  the  texture  and  makes 
the  soil  warmer.  Lime  slaked  with  brine,  marl,  and  gypsum 
arc  generally  useful,  while  carnallite  and  salt  are  valuable 
to  furnish  potash,  soda,  and  chlorine. 


INDEX  OF  AUTHORITIES. 


Abich,  H.,  194 
Adams,  F.  D.,  239 
Agassiz,  L.,  256 
Agricola,  G.,  226 

Barrois,  C.,  2,  178,  324 

Barus,  C.,  104,  241,  326 

Bascom,  Miss  F.,  no 

Bayley,  W.  S.,  167 

Becke,  F.,  178 

Becker,  G.  F.,  94,  130,  208,  274 

Bertels,  G.  A.,  193 

Berghell,  H.,  217 

Berthier,  P.,  377 

Beudant,  M.  F.  S.,  371 

Blandy,  J.  F.,  89 

Blum,  R.,  166 

Bolton,  H.  C.,  12 

Bonney,  T.  G.,  82,  126,  240,  251,  331, 

332 

Boricky,  E.,  12,  218,  219,  233 
Breislak,  S.,  235 

Breithaupt,  A.,  22,   167,  193,  231,  368 
Brogger,  W.  C.,  21,  136,  151,  152,  153, 

156,  164,  166,  171,  241 
Brongniart,  A.,  126,  127,  142,  199,  221, 

247,  249,  261,  337,  378 
Buch,  L.  v.,  154,  189 
Bucking,  H.,  222,  224 

Gallon,  J.,  256 
Cathrein,  A.,  234 
Chamberlin,  T.  C.,  282 
Chelius,  C.,  135,  237 
Chester,  F.  D.,  237 
Chrustschoff,  K,  v.,  133,  161 
Cohen,  E.,  251 

Cole,  G.  A.,  231,  232,  249,  326 
Cossa,  A.,  188 

Cotta,  B.  v.,  124,  131,  135,   136,  142, 
150,  172,  173,  176,  186,  199,  348,  352 
Cross,  W.  C.,  no 


Dana,  E.  S.,  37 

Dana,  J.  D.,  6,  39,  57,  58,  65,  76,  79,  80, 
83,  85,  87,  105,  119,  136,  154,  212, 
263,  270,  275,  277,  278,  326,  328,  344, 
360,  362,  363,  365 

Daubree,  A.,  126 

Daubuisson,  142 

Dechen,  H.  v.,  148 

Deecke,  W.,  216 

Delesse,  A.,  176,  199,  245 

Derby,  O.  A.,  253 

Descloiseaux,  A.,  235 

Dewey,  C.,  26,  344 

Diller,  J.  S.,  230 

Doelter,  C.,  234 

D'Orbigny,  C.,  6 

Drasche,  R.  v.,  203 

Dumas,  E.,  175 

Ehrenberg,  C.  G.,  303,  309 

Elie  de  Beaumont,  174 

Emerson,  B.  K.,  242 

Emmons,  A.  B.,  205,  209 

Emmons,  E.,  356 

Erdmann,  E.,  250,  370 

Esmark,  J.,  238 

Eschwege,  W.  L.  C.  v .,  126,  342,  347 

Fischer,  Dr.,  362 
Foerster,  H.,  184 
Fouque,  F.,  8,  21 
Fournet,  J.,  132 
Fritsch,  K.  v.,  221 

Geikie,  A.,  69,  80,  83,  275,  330,  331, 

333,  341,  369 
Gemmellaro,  C.,  231 
Gerhart,  D.,  142 
Gilbert,  G.  K.,  105 
Gregory,  J.  W.,  249 
Groth,  P.,  130 
Gumbel,    C.  W.,   135,   141,   155,   172, 

173,  188,  201,  241,  250,  271,  286 
401 


4O2 


INDEX   OF  A  UTHORITIES. 


Hague,  A.,   no,  163,  193 

Haidinger,  W.,  319,  376 

Haiiy,  Abbe,  124,  132,   140,   145,   195, 

196,  226,  237,  343,  348,  361 
Haughton,  S.,  337 
Hausmann,  J.  F.  L.,  231,  240,  371 
Hawes,  G.  W.,  130,  153,  211 
Helmhacker,  R.,  139 
Herter,  P.,  112 
Hise,  G.  R.  van,  r,d,  c,$ 
Hitchcock,  C.  H.,  240,  341 
Hobbs,  W.  H.,  184 
Hochstetter,  F.  v.,  250 
Hohenegger,  L.,  242 
Hopkins,  W.,  67 
Home,  J.,  169 

Hunt,  T.  S.,  39,  252,  298,  306,  358 
Hunter,  M.,  155,  169 
Hussak,  E.,  167,  168,  223 

Iddings,  J.  P.,  4,  12,  57,  83,  93,  95,  97, 

i  TO,  230 
Irving,  R.  D.,  237 

Jameson,  R.,  371 

feremejew,  P.  v.,  153 

Jenzsch,  G.,  188 

fohn,  C.  v.,  201 

fudd,  J.  W.,  5,  58,  95,  118,  190,  205, 

231,  232,  251 
Jukes,  J.  B.,  287 

Kalkowsky,   F.,  157,  365,  366 

Kantkiewicz,  S.,  358 

Kemp,  J.  F.,  170,  181,  211 

Keyes,  C.  R.,  40 

Kikuchi,  Y.,  207 

King,  C.,  304 

Kittel,  M.  B.,  134,  135 

Kirwan,  310,  371 

Klaproth,  M.,  158 

Klein,  D.,  10 

Klement,  C.,  13 

Kobell,  F.  v.,  250 

Koch,  A.,  251 

KotO,  B.,  203,  360 

Lametherie,  de,  251 
Lang,  O.,  6,  46,  182 
Lasaulx,  A.  v.,  189 
Laube,  G.  C.,  163 
Leonhard,  K.  C.  v.,  226 
Le  Conte,  J.,  67 
Lenk,  C.,  161 
Lessing,  F.  L.,  4 
Lewis,  H.  Carvill,  250,  282 
Lessen,  K.  A.,  155,  244,  332 


Mann,  P.,  216 
Marsh,  O.  C.,  63,  71,  72 
Merrill,  G.  P.,  304 
Merriman,  M.,  397 
Michel-Levy,  A.,  8,  176,  211 
Mohl,  H.,  234 
Mohs,  F.,  85 

Miigge,  O.,  147,  148,   192,   287,   289. 
2o:> 

Naumann,  C.,  59,  131,  136,  144,  309 
Nordenskiold,  A.,  122,  353 

Orton,  E.,  89 
Osann,  A.,  182,  233 

Pallassou,  Abbe,  242 
Petersen,  J.,  206,  207,  232 
Pettersen,  K.,  367 
Pichler,  A.,  129 
Pisani,  F.,  126 
Pliny,  377 

Rammelsberg,  C.,  216 

Ramsay,  W.,  217 

Rath,  G.  vom,  162,  187 

Reiser,  K.  A.,  241 

Richthofen,    F.    v.,  79,  93,  108,  no, 

153,  191,  208,  289,  306 
Riviere,  A.,  177 
Rohrbach,  C.,  56,  57 
Rose,  G.,  123,  129,  131,  139,  149,  167, 

238,  245 
Rosenbusch,  H.,  21,  34,  39,  46,  56,  57, 

58,  94,  no,  121,  122,  123,   124,  126, 

130,  133,  147,  155.  157,  162,  165,  167, 

169-176,  178,  182,  184,  203,  209,  211, 
214,    215,     2l6,    22O,     225,     233,    242, 

243,  244,  245,  248,  251,  288 
Roth,  J.,  108,  190,  191,  203,  204,  236 
Rutley,  F.,  78,  83,  115,  142,  308 

Salisbury,  R.  D.,  282 
Salvetat,  M.,  309 
Sandberger,  F.,  222 
Sauer,  A.,  152 
Schrauf,  A.,  378 
Senft,  F.,  199 
Simler,  R.  T.,  352 
Sjogren,  H.,  253 
Sorby,  H.  C.,  4,  93 
Stache,  G.,  182,  201 
Steenstrup,  K.,  167 
Stelzner,  A.,  220 
Streng,  A.,  244 
Studer,  B.,  132 
Szabo,  J.,  208 


INDEX  OF  A  UTHORITIES. 


403 


Teall,  J.  J.  H.,  169 

Tornebohm,  A,  E.,  130,  167,  211,  242, 

248,  249 

Townsend,  D.,  83. 
Tschermak,  G.,  137,  141,  199.  206,  250 

Ullman,  J.  C,  371 

Vrba,  K.,  168 

Vogelsang,  H.,  57,  137,  142 

Wadsworth,  M.  E.,  95,  157,  208,  250, 

251,  253 

Walterhausen,  S.  v.,  288 
Weed,  W.  H.,  309 


Weinschenk,  E.,  207 

Weiss,  C.  E.,  348 

Werner,  A.  G.,  126,  371 

Williams,  G.  H.,  4,  57,  in,  153,  229, 

251,  252 

Williams,  J.  F.,  148,  168,  170 
Wright,  G.  F.,  282 

Zinken',  331 

Zirkel,  F.,  20,  21,  39,  84,  94,  109,  no, 
123,  145,  148,  149,  153,  157,  158, 
159,  160,  161,  162,  173,  176,  179,  182, 
183,  185,  194,  198,  201,  203,  204,  208, 

210,  211,  215,  231,  243,  249,  251,  252, 

348,  360 


GENERAL  INDEX. 


Abrasion,  68 

Accessory  ingredients  in  rocks,  7 

Acid  (definition),  4,  85 

—  extrusives,  107-117 

—  intrusives,  117-144 

—  rocks,  4,  85,  99,  107-144 

—  schists,  354 
Acmite,  34 

—  trachyte,  147 
Actinolite,  36 

—  schist,  364 
Adinole,  332,  333 
Adobe,  268 
^Egirite,  34 
^Enigmatite,  38 
Agalmatolite,  26 
Agate,  15 

Age  of  rocks  (relative),  90 
Agglomerated  debris,  264 
Agglomerates,  60 
Akerite,  153 
Alabaster,  294 
Albite,  23 
Algovite,  241 
Allanite,  40 
Allotriomorph,  57 
Alluvium,  267 
Almandite,  48 
Alnoite,  220 
Alpengranit,  132 
Alpenit,  353 
Alsbachite,  135 
Alum  clay,  261 

—  shale,  272 
Amorphous,  58 
Amphibole,  35-38 

—  adinole-schist,  366 

—  and  pyroxene  (comparison),  39 

—  biotite-monchiquite,  170 

—  fourchite,  170 

—  monchiquite,  170 

—  olivine  rock,  369 


Amphibole  ouachitite,  170 

—  rocks,  99,  144 
Amphibolite,  363 
Amygdaloidal,  79 

—  aphanite,  246 

—  porphyry,  140 
Amygdalophyre,  188 
Analcime,  47 
Analcimite,  231 
Anamesite,  226 
Andalusite,  49 

—  hornstone,  331 
Andesine,  24 
Andesite,  189 

—  (hornblende),  191-194 

—  (pyroxene),  203 

—  (quartz),   182-185 
Andesite-diorite  group,  189 
Andesitic  glass,  184,  194 

—  porphyrite,  180 

—  trachyte,  148 
Andradite,  48 
Anhydrite,  294 
Anisotropic,  57 
Anorthite,  24 

—  diorite,  198 

—  gneiss,   353 
Anorthoclase,  20,  21 
Anorthosite,  239 
Anthophyllite,  35 
Anthracite,  319 

—  sand,  270 
Anthraconite,  336 
Apatite,  46,  311 
Aphanite,  246 

—  (diorite),  202 
Aplite,  125 
Apophysis,  105 
Aporhyolite,  no 
Aprons  (glacial),  283 
Aqueous  aggregates,  265 
Arenaceous  rocks,  85 


405 


406 


GENERAL   INDEX. 


Arfvedsonite,  37 
Argillaceous,  85 

—  limestone,  300 

—  pitchstone,  144 

—  shale,  271 
Argillite,  273 

—  (metam orphic),  330 
Argillophyre,  139 
Argiloretinite,  144 
Arkose,  261 

Arrangement  of  eruptive  rocks,  105 

Asbestus,  36 

Aschaffite,  135,  178 

Ash,  284 

Asphalt,  321 

Augite,  33 

—  andesite,  204 
glass,  207 

—  bearing  mica-syenite,  152 

—  camptonite,  211 

—  diorite,  210 

—  free  hornblende-andesite,  193 

—  granite,  131    . 

—  granitite,    130 

—  minette,  175 

—  norite,  239 

—  porphyrite,  245 

—  rock,  367 

—  schist,  368 

—  soda-granite,  131 

—  syenite-porphyry,   157 

—  trachyte,  147 
Augitite,  234 
Aureola,  3,  324 
Automorph,  56 
Automorphic  aggregates,  257-323 

Ball-gabbro,  239 

—  porphyry,  140 
Banatite,  186 
Band  porphyry,  139 
Banded  structure,  83 
Barite,  378 
Barytes,  378 
Basalt,  226 

—  (feldspar),  226 

—  glass,  231 

—  leucite,  219 

—  (magma),  233 

—  (melilite),  220 

—  (nepheline),  218 

—  tuff, 

Basalt-gabbro  group,  224-254 
Basaltic  hornblende,  37 

—  nephenelite,  214 
Basaltoid  leucitite,  215 
Basanite,  221 

—  (leucite),  224 


Basanite  (nepheline),  223 

Basanitoid,  224 

Basic  rocks,  85,  99,  213-254 

—  schists,  355-370 
Bastite,  31 
Bauxite,  379 
Beach  structure,  80 
Bean-ore,  77 

Bed,  80 

Bedded  masses,  80 

—  sheet,  105 
Bedding,  80 

— -  (cloak-like),  81 

—  (false),  80 

—  (trough),  8 1 
Beerbachite,  237 
Beresite,  139 
Bergamaskite,  188 
Biotite,  27 

—  andesite,  193 

—  diorite,  199 

—  gneiss,  351 

—  granite,  129 
porphyry,  135 

—  monchiquite,  160 

—  olivine  rock,  251 

—  quartzite,  333 

—  syenite,  152 

—  —  porphyry,  157 
Bituminous  clay,  261 

—  coal,  317 

—  limestone,  300 

—  shale,  271,  323 

—  wood,  316 
Black  (color),  86 

—  band,  377 

—  chalk,  273 

—  granulite,  349 

—  hematite,  375 

—  lead,  320 

—  porphyry,  187,  244 
Blind  joint,  73 
Blocks,  284 

Blown  sand,  270 
Blue  marbles,  336 

—  porphyry,  185 
Blumengranit,  124 
Bog-head  coal,  318 
Bog  iron-ore,  371 
Bombs,  73,  116,  284 
Bone-beds,  313 

—  breccia,  61,  312 
Boninite,  207 
Borolanite,  169 
Boss,  104 
Bostonite,  155 
Bottlestone,  115 
Bouteillenstein,  115 


GENERAL  INDEX. 


407 


Boulder-clay,  61,  282 
Brandschiefer,  323 
Breccia,  60,  278 

—  (bone),  61,  312 

—  (debris),  262 

—  (oroclastic),  60,  290 

—  (pyroclastic),  60,  284 
Brecciated  conglomerate,  60 
Brecciola,  278 
Brick-clay,  266 
Bronzite,  31 

—  andesite  glass,  207 

—  basalt,  231 

—  diabase,  242 

—  limburgite,  207 

—  norite,  239 

—  olivine-rock,  369 

—  trachyte,  148 
Bronzitite,  252 
Brown  (color),  87 

—  coal,  315 

—  diorite,  210 

—  hematite,  371 
Buchnerite,  251 
Buchonite,  222 
Buhrstone,  277,  341 

Caking  coal,  317 
Calcareous  aphanite,  246 

—  chemical  aggregates,  292 

—  clay-slate,  274 

—  diabase,  242 

—  epidote-schist,  359 

—  mica-schist,  345 

—  organic  aggregates,  297 

—  rocks,  292 

—  sand,  270 
rock,  278 

—  talc-schist,  356 

—  tufa,  304 
Calciphyre,  337 
Calcite,  53 

Camptonite,  176,  211 
Camptonitic  nephelinite,  214 
Candle  coal,  318 
Cancrinite,  42 

—  aegirite-syenite,  167 
Cannel  coal,  318 
Carbonaceous  clay-slate,  273 
Carbonic  shale,  272 
Carnallite,  295 
Carvoeira,  126 
Cataclastic  breccias,  290 
Catawbirite,  376 

Caustic  effects,  325 
Cave-agio  merarte,  264 

—  earth,  312 
Cavernous,  78 


Cellular,  78 
Chabazite,  47 
Chalk,  303 
Chalybeated,  85 

Chemical    aggregates    (automorphic), 
292 

—  (bulk)  analyses,  u 
Cherry  coal,  317 
Chert,  15,  307 
Cherty  limestone,  300 
Chiastolite,  49 

—  slate,  331 
Chlorite,  29 

—  schist,  357 
Chloride  gneiss,  352,  358 

—  granite-porphyry,  136 

—  potstone,  357 

—  slate,  358 
Chloritoid  schist,  358 
Chromic  magnetite,  376 
Chromite,  53 

—  olivine  rock,  369 
Chrysolite,  43 
Cipolino,  336 

Classification  of  rocks,  98,  99 
Clastic,  59 

—  rocks,  257 
Clay,  265 

—  ironstone,  376 

—  slate,  272 

—  stone,  77,  138,  271 

porphyry,  139 

Cleat,  73 
Cleavage,  63 
Cleaved,  82 

Cliff -agglomerate,  264 

Clinkstone,  158 

Clinochlore,  29 

Cloak-like  bedding,  81 

Coal,  317 

Color,  86 

Columnar  jointing,  71 

Compact  syenite,  157 

Comparison  of  pyroxene  and  amphi- 

bole,  38 

Composite  rocks,  7 
Conchoidal  fracture,  85 
Concretion,  76 
Cone  in  cone,  72 
Conglomerate,  60,  278 

—  schist,  342 
Contact-metamorphism,  324 

—  zones,  324 
Convergence,  69 
Cooling,  64 
Copper-slate,  307 
Coprolite  beds,  313 
Coquina,  66,  278 


4o8 


GENERAL  INDEX. 


Coral  chalk,  303 
Cordierite,  47 

—  gneiss,  352 

—  granite,  125 
Cornubianite,  331 
Corsite,  198 
Cortlandtite,  251 
Corundum,  51 
Cossyrite,  38 
Crumbly  fracture,  86 
Cryolite,  295 
Cryptocrystalline,  58 
Cryptomeric,  61 
Cryptoperthite,  21 
Crystal,  56 

—  sand,  270 
Crystalline,  58 

—  granular,  58 

—  limestone,  334 

—  rocks,  329 

—  schists,  337 
Crystalloid,  58 
Cumberlandite,  253 
Current-bedding,  80 
Cuselite,  245 
Cyanite,  50 

—  rock,  362 

Dacite,  182-185 

—  felsite,  184 

—  glass,  184 

—  obsidian,  185 

—  pitchstone-porphyry,  185 

—  pumice,  185 
Damascened,   78 
Damourite,  26 

—  schist,  344 
Debris,   259-264 

—  breccia,  280 

—  clays, 261 

—  in  place,  260-263 

—  sands,  260 

—  slightly  moved,  263-264 
Desmosite,  331 
Devitrification,  62 
Diabase.  240 

—  aphanite,  246 

—  glass,  248 

—  gneiss,  353 

—  pegmatite,  241 

—  porphyrite,  244 
Diallage,  33 

—  andesite,  206 

—  granulite,  348 

—  hypersthene  rock,  367 

—  rock.  367 
Diallagite,  235,  252 
Diamond-sand,  269 


Diatoms,  18 
Diatom  earth,  308 

—  mud,  309 
Dichroite  (iolite),  46 

—  gneiss,  352 

—  granite,  125 

Differentiation  of  magmas,  4,  92 
Dike,  2,  104,  105 

—  metamorphism,  325 

—  sandstone,  279 

—  (stepped),  105 
Diopside,  32 
Diorite,  195-200 

—  aphanite,  202 

—  (brown),  210 

—  glass,  188 

—  gneiss,  352 

—  mica  -  hornblende  -  pitchstone  por- 
phyry, 189 

—  mica-pitchstone  porphyry,  188 

—  (orbicular),  198 

—  porphyrite,  200 

—  (pyroxene),  209 

—  (scapolite),  198 

—  schist,  364 

Diorite-quartzifera-porfiroide,  188 
Dioritic  mica-trap,  176 

—  lamprophyre,  176 
Dipyre-slate,  331 
Dirt-bed,  264 
Disthene,  50 

—  rock,  362 
Ditroite,  168 
Dolerine,  356 
Dolerite,  226 
Doleritic  nephelinite,  214 
Dolomite,  54,  305 
Dolomitic  limestone,  299 
Domite,  147 

Drusy,  79 

—  porphyry,   140 
Drying,  64 
Dunite,   250 
Durbachite,  152 
Dysodile,  316 

Eclogite,  361 

—  amphibolite,  361 
Economic  value  of  rocks,  392 
Egeran-schist,  368 
Ehrwaldite,  234 

Elaeolite,  41 

—  syenite,  164 

porphyry,  170 

Elvan,  136 
Emery,  52 
Enstatite,  30 

—  andesite,  206 


GENERAL   INDEX. 


409 


Enstatite  diabase,  242 

—  olivine  rock,  369 

—  porphyrite,  244 

—  rock,  366 
Epidosite,  248,  358 
Epidote,   39-41 

—  actinolite-schist,  364 

—  glaucophane-schist,  365 

—  granite,  128 

—  schist,  359 

—  syenite,  151 
Epistilbite,  46 
Erlan,  368 
Erratics,  280 

Eruptive  agglomerate,  264 

—  rocks,  6,  93,  95 

Essential  ingredients  (in  rocks),  7 

Etched,  59,  65,  73 

Eudyalite-syenite,  168 

Eukrite,  243 

Eulysite,  250,  370 

Euphotide,  237 

Eurite,  142 

External  structure,  71 

Extruded  sheet,  105 

Extrusive,  95 

—  rocks,  103 
Eye-stones,  77 

Fairy  stones,  77 
False-bedding,  80 
Fat-clay,  266 
Fault,  64 
Fayalite,  44 
Felshe,   142 

—  porphyry,  137,  141 
Felsitic,  84 

—  hornstone,  331 
Feldspar,  18 

—  amphibolite,  363 

—  basalt,  226 

—  biotite-quarzile,  333 

—  (decomposition  of),  379 

—  magma-basalt,  233 
Feldspathic  ash,  286 
Feldspathoid  magma-basalt,  233 
Felsophyre,  57 
Felsophyric,  85 

Felstone,  142 

—  porphyry,   139 
Ferrite,  54 

Ferruginous-organic  aggregates,  323 
Fetid  limestone,  300 
Feuerstein,  307 

Fibrolite,  50 
Fibrous,  84 
Filiform,  72 
Fiorite,  18,  309 


Fire-clay,  266 
Firn,  297 
Fissile,  82 
Fissured,  81 
Flagband-cleavage,  83 
Flagstone,  276 

—  cleavage,  83 
Flat-parallel  structures,   80 
Flexible  sandstone,  342 
Flint,  19,  307 

Flow-and-plunge  structure,  80 
Fluidal,  83 

Fluorite,  295 
Fluxion  structure,  83 
Foliated,  82 
Forellenstein,  240 
Forest-soil,  263 
Fourchite.  170 
Foyaite,  166 
Fracture,  85 
Fractured,  82 
Fragmental  rocks,  257 
Fraidronite,  175 
Franklinite,  377 
Free  convergence,  69 

—  stone,  277 

Friction-breccias,  284,  290 
Fruit-slate,  332 
Fulgurite,  84 

Fuller's  earth,  267 

Fusing  point  of  rocks,  104 

Gabbro,  235 

—  diorite,  211 

—  glass,  248 

—  gneiss,  353 

—  granite,  130,  237 

—  schalstein,  290 
Ganister,  277 
Garnet,  48 

—  olivine-rock,  369 

—  rock,  360 

Garnetiferous  magnetite,  376 
Garnetyte,  360 

Gedrite,  35 

General  definitions,  55 

Geodesy,  6 

Geodic,  79 

Geology,  6 

Geyserite,    18,  309 

Giallo-antico,  335 

Giant  gneiss,  351 

Gieseckite-porphyry,  171 

Gilsonite,  321 

Glacial  aggregations,  75,  280-283 

Glaciated,  59,  68,  74 

Glacier-ice,  297 

Glassy,  61 


GENERAL  INDEX. 


Glauconitic  sandrock,  278 
Glaucophane,  37 

—  augite-schist,  368 

—  epidosite,  359 

—  schist,  365 
Globuliferous,  79 
Gneiss,  349 

—  (augen),  351 

—  (chloritic),  352 

—  (dichroite),  352 

—  (hornblende),  352 

—  (mica),  351 

—  (porphyritic),  351 

—  (syenite),  352 
Gold-bearing  sand,  269 
Graniodiorite,  130 
Granite,  117-134 

—  gneiss,  351 

—  laterite,  263 

—  porphyry,  134 
Granitell,   125 

Granitic  granite-porphpry,  135 
Granitite,  129 
Granitoid,  59 

—  hornblende-andesite,  192 

—  rhyolite,  no 
Granitone,  235 
Granophyre,  57 
Granular,  58 
Granulite,  348 

—  gneiss,   352 

—  (pyroxene),  348 
Graphic  granite,  84,  124 
Graphite,  320 
Gravel,  279 

Gray  gneiss,  352 

—  trachyte,  191 
Green  (color),  87 

—  porphyry,   136 
Greenstone,  196 

—  like  porphyrite,  177 

—  trachyte,  208 
Greisen,  128 
Grit,  57,  276 
Grorudite,  136 
Grossularite,  48 
Ground-ice,  297 

—  moraine,  282 
Groundmass,  57 
Guano,  313 
Guinea-quartz,  17 
Gypsum,  293 

Halbgranit,  125 
Halleflinta,  353 
Haloidal  aggregates,  293 
Hard  coal,  317 
Hardness,  85 


Hardpan,  279 
Harmotome,  47 
Harzburgite,  251 
Haselgebirge,  264 
Haiiyne,  43 

—  tachylite,  234 

—  tephrite,  222 

—  trachyte,  149,  161 
Haiiynophyre,  216 
Heavy  spar,  378 
Heat  transmission,  53 
Hemithrene,  199 
Heulandite,  46 
Hiortdahlite,  34 
Hislopite,  337 
Holocrystalline,  57 
Hornblende,  37 

—  andesite,  191 
— . —  glass,  194 
pumice,  194 

—  (basaltic),  37 

—  epidote-schist,  359 

—  gabbro,  237 

—  gneiss,  352 

—  granite,  131 

—  porphyrite,  200 
porphyry,  136 

—  granitite,  130 

—  mica-elaeolite-syenite,  168 

—  minette,  175 

—  nepheline-tephrite,  222 

—  norite,  239 

—  picrite,  251 

—  porphyrite,  200 

—  pyroxene-elseolite-syenite,  166 
porphyry,   171 

—  quartz-porphyry,  141 

—  rocks,  144-212 

—  schist,  363 

—  syenite,  151 

—  syenite-porphyry,  156 
Hornblendite,   212 
Hornschiefer,  366 
Hornstone,  15,  307 

—  (felsitic),  331 

—  porphyry,  139 

—  (tourmaline),  333,  346 
Hudsonite,  251 
Hyalite,  17 
Hyalomelane,  231 
Hyalomicte,  128 
Hyalosiderite,  44 
Hyalotourmalithe,   126 
Hydraulic-limestone,  300 
Hydrogenic  aggregates,  259 
Hydromica-schist,  344 
Hydrotachylite,  232 
Hyperite-porphyrite,  244 


GENERAL  INDEX. 


411 


Hypersthene,  31 

—  andesite,  206 

—  basalt,  230 

—  diabase,  242 

—  diorite,  210 

—  gabbro,  237 

—  granulite,  348 

—  hornblende-andesite,  193 

—  norite,  239 

—  quartz-porphyrite,  244 

—  syenite,  153 

—  trachyte,  148 
Hysterobase,  241 

Ice,  296 
Idiomorph,  56 
liolite,  217 
Ilmenite,  375 
Imatra-stone,  77 
Implication  structure,  84 
Impregnation,  68 
Indianaite,  379 
Individualized  matter,  55 
Infusorial  earth,  308 
—  meal,  309 
Intermediate  rocks,  99,  144 

Internal  structures,  78 

Intratelluric  crystallization,  58,  94 

Intruded  sheet,  105 

Intrusive,  95 

lolite,  47 

Iron  ores,  296 

Irregular  fracture,  86 

Isenite,  193 

Iserine,  375 

Isotropic  groundmass,  57 

Itabarite^  347 

Itacolumite,  342 

Jacotinga,  347 
Jacupirangite,  253 
Jade,  36 

Jadeglanduleux,  249 
Jasper,  15 
Jet,  318 
Jointed,  63,  72 

Kalkaphanit,  246 
Kalkdiorit,  199 
Kalkgranit,  129 

—  pistacit  schist,  359 

—  tuff,  304 
Kammgranit,  130 
Kaolin,  379 
Keratophyre,  141,  155 
Kerosene,  322 
Kersantite,  177 


Kersanton,  177 
Kieselguhr,  309 
Kimberlite,  250 
Kinzigite,  362 
Klein's  solution,  IO 
Knotty-slate,  330 
Kunkurs,  77 

Laacher  trachyte,  148 
Labrador-porphyrite,  245 
Labradiorite,  199 
Labradorite,  24 
Laccolith,  105 
Laminated,  82 
Lamprophyre,  172-178 
Lapilli,  284 

Lateral  moraine-stuff,  281 
Laterite,  262 
Lathy,  84 
Laumontite,  46 
Laurdalite,  164 
Laurvikite,  152 
Lava-sperone,  215 

—  stream,  105 
Leaf -coal,  316 
Lean-clay,  266 
Lenticular  masses,  80 
Lepidolite,  26 
Lepidomelane,  28 
Leptynite,  348 
Leptynolite,  331 
Leuciite,  198 
Leucite,  41 

—  anamesite,  219 

—  basalt,  219 

—  basanite,  224 

perlite,   obsidian,   and    pumice, 

232 

—  dolerite,  219  _ 

—  elaeolite-syenite,  168 
porphyry,  171 

—  nepheline-trachyte,  162 

—  phonolite,  162 
pumice.  163 

—  tephrite,  223 

—  trachyte,  162 
Leucitite,  215 
Leucitoid  basalt,  219 
Leucitophyre,  162,  224 
Leucophyre,  224,  241 
Lherzolite,  251 
Liebnerite-porphyry,  171 
Lignite,  315 
Limburgite,  233 
Lime-granite,  129 

—  silicate-hornstone,  333 
Limestone,  297 

—  (crystalline),  334 


412 


GENERAL  INDEX. 


Limonite,  371 

Linear-parallel  structures,  80,  84 

Liparite,  no 

Listwenite,  356 

Litchfieldite,  167 

Lithionite,  27 

Lithographic  limestone,  301 

Lithoid,  61 

Lithoidite,  no 

Lithology,  6 

Lithopysae,  70,  79 

Lithophysic  obsidian,  115 

Lithosphere,  6 

Loam,  263 

Local  metamorphism,  324 

Loess,  268 

Lucullite,  336 

Luxullianite,  126 

Lydian  stone,  343 

Magma  basalt,  233 
Magnesian  limestone,  305 
Magnesite,  378 
Magnetite,  52 

—  olivenite,  253 

—  rock,  375 

—  sand,  269 

—  series,  252 
Malacolite,  32 

—  rock,  367 
Malchite,  182 
Mamelon,  104 
Mandelato,  333 
Manganese-epidote-schist,  360 
Marble,  334 

Marekanite,  112 

Margarite,  29 

Margarophyllite  group  (schists),  355 

Marl,  306 

Massive,  78,  80 

—  rocks,  92 

Mechanical  aggregates,  258-292 
Melanite,  47 

—  elaeolite-syenite,  169 
Melaphyre,  247 
Melilite,  43 

—  basalt,  220 
Menaccanite,  375 
Meta-anthracite,  320 
Metamorphic  argillite,  330 

—  crystalline-schists,  337 

—  limestone,  333 

—  phyllite,  332 

—  rocks.  324,  337 

—  sandstone,  333 

—  schists,  337 

—  zones,  324 
Metamorphism,  324 


Metamorphism  (contact,  or  local),  324 

—  (regional),  327 
Metamorphosed  schists,  333 
Mexican  onyx,  304 
Miarolite,  132 
Miarolitic,  59,  133 
Miascite,  167 

Mica,  25-29 

—  andalusite-slate,  332 

—  andesite,  193 

—  augite-porphyrite,  245 

—  basalt,  229 

—  dacite,  184 

—  diabase,  242 

—  diorite,  199 
porphyrite,  202 

—  elaeolite-syenite,  167 

—  epidote-schist,  359 

—  gabbro,  237 

—  gneiss,  351 

—  hornblendite,  212 

—  (hydro-),  26 

—  leucitite,  216 

—  magma-basalt,  233 

—  norite,  239 

—  phyllite,  332 

—  porphyrite,  178,  181 

—  (quartz-),  diorite,  187 

—  rocks,  99,  107 

—  schist,  343 

—  slate,  343 

—  syenite,  152 

—  trap  rocks,  172-178 
Micaceous  clay-slate,  274 

—  hematite,  374 

—  iron-schist,  347 

—  shale,  272 
Microchemical  tests,  12 
Microclastic,  59 
Microcline,  20 
Microcrystalline,  59 
Microgranitic,  57 
Micropegmatitic,  57 
Microperthite,  21 
Micropoikilitic,  58 
Microsyenite,  157 
Migration -structure,  286 
Mijakite,  206 

Millstone-porphyry,  no,  140 
Mineral  oil,  322 

—  pitch,  321 

—  wax.  322 
Mineralizing,  125,  325 
Minerals  as  rocks,  371-381 

—  (necessary)  for  primary  rocks,  98 

—  (rock-forming),  14 
Minette,  174 
Mining,  261 


GENERAL  INDEX. 


413 


Moja.  288 
Moldauite,   115 
Monazite,  51 
Monchiquite,    169 
Monzonite,  239 
Moor-coal,  316 
Moraine-stuff,  61,  281 
Mud,  267 
Mudstone,  267 
Murasaki,  360 
Muscovite,  25 

—  biotite-granite,  123 

—  gneiss,  351 

—  granite,   124 

Nacritide,  345 

Nadeldiorit,  198 

Napcleonite,  198 

Natrolite,  47 

Navite,  248 

Necessary  ingredients  to  rocks,  7,  98 

Neck,  103 

Needle-coal,  316 

Nepheline,  41 

—  anamesite,  218 

—  basanite,   223 

—  basalt,  218 

—  dolerite,  218 

—  olivine- jacupirangite,  253 

—  rhomb-porphyry,  171 

—  tephrite,  221 

—  trachyte,   158 
Nephelinite,  214 
Nephelinitoid  basalt,  218 
Nephrite,  37 
Nero-antico,  336 
Nevadite,  no 

Neve,  296 

Non-caking  coal,  317 
Nordmarkite,  151 
Norite,  238 

—  aphanite,  246 

—  gneiss,   353 

—  porphyrite,  243 
Nosean,  43 

—  melanite-rock,  162 

—  phonolite,  161 

—  trachyte,   161 
Noseanite,  219 
Novaculite,  308 
Nyirock,  263 

Obsidian,  114 

—  bombs,  116 

—  perlite,  112 

—  pumice,    116 
Odinite,  237 
Oil-shale,  323 


Oligoclase,  23 
Olivine,  43 

—  diabase,  243 

—  enstatite-gabbro,  238 

—  gabbro,  238 

—  kersantite,  178 

—  less  basalt,  231 

—  leucite-phonolite,  163 

—  norite,  239 
porphyrite,  244 

—  proterobase>   243 

—  pyroxene-andesite,  206 

—  rock,  369 

—  schist,  370 

—  series,  249 
Olivineless  basalt,  230 
Ollenite,  364 
Omphacite,  34 

—  rock,  367 

—  zoisite-rock,  359 
Oolite,  305 
Oolitic,  76 

—  ice,  296 

—  quartzite,  341 
Opacite,  54 
Opal,  17 
Ophicalcite,  336 
Ophite,   242 
Orbicular  diorite,  198 
Ordinary  clay-slate,  273 
Ore-pots,  77 

Organic  aggregates,  297 
Oroclastic  breccias,  60,  290 
Orogenic  rocks,  289 
Orthoclase,  18 

—  gabbro,  237 

—  monzonite,  152 
Orthophyre,  153,  154 
Ortlerite,  201 
Ossipyt,  240 
Osteolite,  311 
Ottrelite,  29 

—  slate,  331 
Ouachitite,  170 
Ozokerite,  322 

Paint-clay,  266 
Palaeophyre,  188 
Palaeopicrite,  250 
Palagonite-tuff,  288 
Pantellerite,  184 

—  glass,  185 
Paper-coal,  316 
Parabasalt,  231 
Paragonite,  26 

—  schist,  344 
Parallel  structures,  80 
Paramorphs,  8 


414 


GENERAL  INDEX. 


Pargasite,  37 
Parorthoclase,  20,  21 
Parrot  coal,  318 
Pausilippo,  288 
Peat,   314 

Pebble-phosphate,  311 
Pegmatite,  124 
Pele's  hair,  72 
Pelites,  59 
Pencil  slate,  273 
Penninite,  30 
Peperin  basalt,  219 
Peperino,  288 
Peridot,  43 
Peridotite,  249 
Perlite,  in 
Perlitic,  79 

—  dacite,  185 
pumice,  185 

—  hornblende-andesite,  194 

pitchstone,  194 

pumice,  194 

—  pitchstone,  113 

—  pumice,  116 
Perthite,  19 
Petrography,  7 
Petroleum,  322 
Petrosjlex,  142 
Phanerocrystalline,  58 
Phenocryst,  57 
Phillipsite,  47 
Phlogopite,  28 
Phonolite,  158 

—  obsidian,   163 

—  pitchstone,  163 

—  tephrite,  222 
Phonolitic  trachyte,  148 
Phosphate  rock,  311 
Phosphatic  aggregates,  310 

—  chalk,  311 
Phosphorite,  310 
Phthanite,  307,  343 
Phyllite,  29,  274 

—  (metamorphic),  332 

—  proper,  274 
Phytogenic  limestone,  303 

—  rocks,  303,  314 
Picrite,  250 
Piedmontite,  40 

—  schist,  360 
Pietra  verde,  289 
Pilite  kersantite,  178 
Pinsill,  273 
Pipe-clay,  266 

—  ore,  77 
Pisolite,  305 
Pisolitic,  76 
Pistacite  rock,  358 


Pit-coal,  317 
Pitch-coal,  316 
Pitchstone,  143 

—  felsite,  144 

—  peperite,  188 

—  (perlitic),  113 

—  porphyry,  142 

—  (rhyolitic),  113 

—  (trachytic),  113 
Plagioclase,  21-24 

—  gneiss,  353 

—  olivene-magnetite,  253 

—  porphyrite,  178,  181 

—  pyroxene- magnetite,  253 
Plagiophyre,  57 

Plastic  clay,  266 
Plug,  103 
Poikilitic,  58 
Polirschiefer,  309 
Polishing-slate,  309 
Porcelain,  379 

—  jasper,  330 
Porcellanite,  330 
Porfido  rosso, antico,  201 

—  verde  antico,  245 
Porous,  78 

—  porphyry,  140 
Porphyrite,  178,  181 
Porphyritic,  58 

—  obsidian,  115 

—  perlite,  112 

—  phonolite,  160 

—  pumice,  116 
Porphyroid  (rock),  354 

—  texture,  57 
Porphyry,  57 

—  like  porphyrite,  180 
Potato-stone,  239 
Potstone,  357 
Pozzulana,  284 
Prasenite,  366 
Predazzite,  337 
Preliminary  definitions,  6 
Pressure,  63 

Primary  minerals,  8 

—  rocks,  97 

(general  divisions),  106 

Prochlorite,  30 
Propylite,  208 

—  porphyrite,  201 

—  (quartz),  208 
Proteolite,  331,  332 
Proterobase,  241 
Protogine  gneiss,  352 

—  granite,  132 
Psammites,  59 
Psephites,  59 
Pseudochrysolite,  115 


GENERAL   INDEX. 


415 


Pseudofluidal  structure,  286 
Pseudomorphs,  8 
Pudding-granite,  133 

—  stone,  60,  278 
Pulaskite,  168 
Pumice,  116 

—  (basalt),  232 

—  (leucite-phonolite),  163 

—  (rhyolite),  116 

—  sand,  270 

—  (trachyte),  117 
Pumiceous,  79 

—  pitchstone,  114 
Puy,  104 
Pyrites,  380 

Pyritiferous  porphyry,  139 
Pyroclast,  60,  283 
Pyroclastic  breccia,  60,  284 
Pyrogenic  aggregates,  283 
Pyromeride,  140 
Pyrope,  48 
Pyropissite,  316 
Pyrophyllite,  45 

—  schist,  358 
Pyroxene,  30-34 

—  and  amphibole  (comparison),  39 

—  andesite,  203 
glass,  207 

—  diorite,  209 

—  gneiss,  353 

—  granite-porphyry,  136 

—  granulite,  348 

—  magnetite,  253 

—  quartz-porphyry,  141 

—  rock,  366 

—  rocks,  99,  213-255 

—  schist,  367 

—  syenite,  152 
Pyroxenite  (of  Hunt),  252 

—  (of  Coquand),  367 

Quartz,  15 

—  andesite,  182-185 

—  augite-andesite,  206 
diorite,  210 

—  basalt,  230 

—  diorite,  186 

—  hornblende-diorite,  186 
porphyrite,  187 

—  keratophyre,  155 

—  kersantite,  178 

—  mica-andesite,  184 

—  mica-diorite,  187 
prophyrite,  181 

hornblende-porphyrite,  188 

—  norite,  239 

—  porphyry,  136-141 


Quartz  propylite,  208 

—  schist,  341 

Buartzite,  340 
uartzless  orthoclase  porphyry,  154 
Quartzophyre,  57 

Radiolarian  ooze,  18,  308 
Randanite,  309 
Rapakivi,  130 
Rattle-stones,  65,  77 
Red  gneiss,  351 

—  hematite,  373 

—  marbles,  335 
Regional  breccia,  291 

—  metamorphism,  327 
Relative  age  of  rocks,  90 
Rensselaerite,  356 
Replacement,  88 
Restrained  convergence,  70 
Retinite,  143 

Rhyolite,  108 

—  granite  group,  107 
Rhyolitic  glass,  in 

—  obsidian,  114 

—  perlite,  in 

—  pitchstone,  113 
Rhomb  porphyry,  154 
Ribbon-gneiss,  351 
Riebeckite,  38 
Rock,  6,  7 

—  (composite),  7 

—  forming  minerals,  14 

—  meal,  282 

—  salt,  294 

—  (simple),  7 
Roestone,  305 
Rolled,  59,  68,  74 
Roofing-slate,  273 
Rottenstone,  302 
Rubellan,  28 

Sagvandite,  367 
Sahlite-diabase,  242 
Saliferous  clay,  261 
Sand,  268 

—  coal,  317 

—  rock,  277 

—  stone,  275 

laterite,  263 

Sandy  limestone,  301 
Sanidine,  19 

—  bombs,  149 

—  quartz- porphyry,  141 
Sanidinite,  149 
Sanukite,  2^7 
Sapphire,  51 
Saugschiefer,  309 


4i6 


GENERAL   INDEX. 


Saussurite,  39 

—  gabbro,  237 
Saxonite,  250 
Scapolite,  47 

—  diorite,  198 
Schalstein,  242,  290 

Scheme  for  determining  the  principal 

rocks,  282-391 
Schieferletten,  271 
Schist,  82 
Schistoid  elaeolite-syenite,  169 

—  gabbro,  236 

—  granite,  133 
Schistose,  82 
Scoriaceous,  79 
Scyelite,  251 
Seams,  80 

Secondary  minerals,  8,  256 

—  rocks,  6,  255 
Secretion,  69 
Sedimentary  crystallization,  70 

—  rocks,  264 
Sedimentation,  67 
Segregation,  69,  70 
Semi-athracite,  319 

—  bituminous  coal,  318 
Separation  of  minerals,  9-10 
Septaria,  77 

Sericite  gneiss,  352 
Sericite-phyllite,  332 
Serpentine,  44,  254,  377 

—  sandrock,  278 
Shale,  271 
Shaly,  82 

—  lamination,  83 
Sharp,  59 
Shear,  63 

—  zone  breccia,  290 
Sheet,  105 

Shell  limestone,  302 
Shingle,  61,  279 
Siderite,  376 
Sideromelane,  288 
Sienna  marble,  335 
Siliceous  hematite,  375 

—  limestone,  300 

—  schist,  343 

—  sinter,  309 

—  tufa,  309 

Silicified  tuffs,  breccias,  etc.,  290 
Silicophite,  378 
Sill,  105 
Sillimanite,  50 

—  biotite-quartzite,  333 
Silt,  267 

Simple  rocks,  7 
Slack-water  clay,  283 
Slate,  272,  274 


Slate  gneiss,  351 
Slaty,  82 

—  porphyry,  139 
Slickensides,  63,  81 
Slope  agglomerate,  264 
Smaragdite,  36 

—  gabbro,  237 
Smooth  fracture,  86 
Snow  ice,  296 
Snowflake  marble,  336 
Soapstone,  356 
Soda-orthoclase-quartz-porphyry,  141 

—  rhyolite,  no 
Sodalite,  42 

—  syenite,  167 
Soft  coal,  317 

—  ore,  262 
Solution,  65 
Sordawalite,  249 
Spathic  iron,  376 
Spectacle-stones,  77 
Specular  hematite,  374 

—  iron,  373 
Sperone,  215 
Spessartite,  48 
Sphserosiderite,  376 
Spherical  structures,  78 
Spheroidal,  73 

—  norite,  239 
Spherophyric,  79 

—  granite,  133 

—  obsidian,  115 
Spherulitic,  79 
Spilite,  246 
Spilosite,  331 
Splint-coal,  317 
Splintery  fracture,  86 
Spotted  basalt,  230 

—  phonolite,  160 
Sprudelstein,  305 
Stalactite,  72,  293 
Stalagmite,  293 
Statuary  marble,  335 
Staurolite,  51 

—  slate,  331 
Steatite,  356 
Stepped  dike,  105 
Stilbite,  47 
Stinkstone,  300 
Stone-coal,  317 
Straticulate,  80 
Stratified,  68,  80 

—  aqueous  deposits,  265 
Streaked,  83 

Striped  porphyry,  139 
Structural  agents,  61-70 
Structures,  62-84 
Stylolites.  63,  71 


GENERAL   INDEX. 


417 


Subangular,  73 

Sudden  changes  in  rocks,  i 

Suldenite,  201 

Sulphur,  380 

Swinestone,  300 

Syenite,  149 

—  aphanite,  157 

—  gneiss,  352 

—  porphyry,  156 

—  trachyte  group,  145 
Syenitic  mica  traps,  174 

—  granite,  131 

—  lamprophyres,  174 
—  porphyries,  I53-I57 
Syenitporphyr,  136 

Tabular  fracture,  86 
Tachylite.  231 
Taimyrite,  161 
Talc,  45 

—  amphibole  schist,  364 

—  schist,  355 
Tennessee  marble,  336 
Tephrite,  221 
Tephritoid,  222 

—  leucitite,  215 
Terminal  moraine,  282 
Terrane,  6 
Teschenite,  225,  242 
Textures,  55-61 
Theralite,  225 
Thinolite,  304 
Tile-clay,  266 

Till,  6t ' 

Timazite,  183,  193 
Tin-granite,  128 

—  sand,  269 
Tinguaite,    167,  171 
Tiree  marble,  335 
Titaniferous  iron-ore,  375 
Tonalite,  187 

—  gneiss,  352 
Topaz,  49 

—  brokenfels,  347 

—  rock,  127 
Topazfels,  127 
Topazoseme,  127 
Torbanite,  308 
Tosca,  288 
Touchstone,  343 
Tourmaline,  50 

—  granite,  126 

—  hornstone,  333,  346 

—  quartz  ite,  127 

—  rock,  127 

—  schist,  333,   346 
Trachydolerite,  194 


Trachyte,   145 

—  glass,  in 

—  pumice,  117 

—  syenite  rocks,  145 
Trachytic  obsidian,  115 

—  perlite,  112 

—  pitchstone,  113 

—  pumice,  116 
Trass,  288 
Travertine,  303 
Tremolite,  36 
Tridyrnite,  16 
Tripestone,  294 
Tripoli,  309 
Troctolite,  240 
Trough-bedding,  81 
Trowlesworthite,  126 
Tufa  (calcareous),  304 

—  laterite,  263 

—  (siliceous),  309 
Tuffs,  285 
Tuffite,  289 
Tuffoid,  290 
Turf,  314 
Typical  gneiss,  351 

—  obsidian,  114 

—  phonolite,  158 

—  quartz-porphyry,  138 

—  trachyte,  147 

Uintaite,  321 
Unakite,  128 

Unindividualized  matter,  55 
Unsorted  debris,  259-264 
Uralite,  36 

—  diabase,  242 

—  porphyry,  245 

—  schist,  358 

—  syenite,  153 
Uvarovite,  48 

Variolite,  249 
Variolitic  granite,  133 
Veined,  81 
Verde  antique.  336 
Verite,  233 
Vesicular,  79 

—  crystallization,  70 

—  obsidian,  115 

—  perlite,  112 

—  phonolite,  160 

—  porphyry,  140 
Vesuvianite,  49 

—  augite-schist,  368 

—  schist,  368 
Viridite,  54 
Vitreous,  61 


4i8 


GENERAL   INDEX. 


Vitriol-peat,  315 
Vhrophyre,  57,  142 
Volcanic  ash,  etc.,  283 

—  glass,  114 
Volcanite,  184 
Vosgesite,  175 

Wacke,  263 
Water-ice,  297 
Wax  coal,  315 
Weathering,  65,  255 
Websterite,  252 
Wehrlite,  250 
Wernerite,  47 
Whetslate,  308 
Whetstone,  308 
White  (color),  86 

—  porphyry,  139 
Wichtisite,  248 


Wind-drift  structure,  80 
Winooski  marble,  336 
Wood-gneiss,  351 

Xenomorph,  56 
Yellow  (color),  87 

Zeolites,  46 
Zinnwaldite,  27 
Zircon,  45 

—  syenite,  168 
Zobtenite,  236 
Zoisite,  39 

—  diallage  rock,  367 
Zones  (metamorphk),  324 
Zoogenic  limestone,  298 

—  rocks,  297    307,  310 
Zweiglimmeriger  granit,  123 
Zwitter  rock,  128 


DESCRIPTION    OF    THE    PLATES. 

The  cuts  of  Plates  I,  II,  and  I  to  4  of  VI  are  5/6  natural 
scale  ;  5  and  6  of  IV  are  3/4  the  same ;  and  6  of  V  is  1/20  the 
same ;  the  rest  are  of  natural  scale. 

PLATE  I. 

1.  Medium-crystalline-granular  (granitoid)  porphyritic  granite. 

2.  Pudding-granite  with  concretions  of  predominant  mica. 

3.  Granitoid  olivine-diabase. 

4.  Fine-crystalline-granular  diabase. 

5.  Similar  leucite-tephrite,  with  phenocrysts  of  leucito. 

6.  Fine-crystalline-granular  and  porphyritic  dacite. 

PLATE  II. 

1.  Porphyritic  hornblende-granitite. 

2.  Luxullionite. 

3.  Coarse-granular  elaeolite-syenite. 

4.  Porphyritic  dolorite. 

5.  Oligoclase-porphyrite. 

6.  Orthoclase- porphyry. 

PLATE  III. 

1.  Orbicular  diorite. 

2.  Pegmatite. 

3.  Fine-crystalline  hypersthene-andesite  (vesicular). 

4.  Microcrystalline  rhyollte  (vesicular  and  porous). 

5.  Microcrystalline  limburgite  (amygdaloidal). 

6.  Microcrystalline  quartz-porphyry  (vesicular  oorous  pyroclastic  breccia). 

PLATE  !V. 

1.  Perlite  (perlitic). 

2.  Obsidian  (vitreous). 

3.  Tachylite  (scoriaceous). 

4.  Olivine-rock  (volcanic  bomb). 

5.  Halleflinta  (fluidal). 

6.  "  Bastkohl  "  (fibrous). 

PLATE  V. 

1.  Limestone  (oolitic). 

2.  Quartz-conglomerate  (pudding-stone). 

3.  Brecciola. 

4.  Rolled  sand  (river). 

5.  Sharp  sand  (glacial  rock-meal). 

6.  Till  (crushed  slate  with  angular  debris  and  rolled  sand,  gravel,  etc.), 

PLATE  VI. 

1.  Clay-slate  (slaty  cleavage  from  pressure). 

2.  Calcareous  mica-schist  (flat- parallel). 

3.  Calcareous  mica-schist  (lenticular-parallel). 

4.  Hornblende-schist  (irregular). 

5.  Gneiss  (foliation). 

6.  Gneiss  (segregation  in  strings). 


PLATE  L 


PLATE  IL 


PLATE  111. 


PLATE  IV. 


PLATE   V. 


m 


PLATE   VI, 


SHORT-TITLE     CATALOGUE 

OF  THE 

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12 


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Part  III. — A  Treatise  on  Brasses,  Bronzes  and  Other  Alloys 

and  their  Constituents 8vo,  2  50 

Thurston's  Text-book  of  the  Materials  of  Construction.  ..  .8vo,  5  00 
Wood's  Treatise  on  the  Resistance  of  Materials  and   an   Ap- 
pendix on  the  Preservation  of  Timber 8vo,  2  00 

"        Elements  of  Analytical  Mechanics 8vo,  3  00 

STEAM  ENGINES  AND  BOILERS. 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.) 

12mo,     1  50 
Dawson's  "  Engineering  "  and  Electric  Traction  Pocket-book. 

16mo,  morocco,    4  00 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,     1  00 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy. 

12mo,    2  00 

Button's  Mechanical  Engineering  of  Power  Plants 8vo,    5  00 

"        Heat  and  Heat-engines 8vo,     5  00 

Kent's  Steam-boiler  Economy 8vo,     4  00 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,     1  50 

MacCord's    Slide-valves 8vo,    2  00 

Meyer's  Modern  Locomotive  Construction 4to,  10  00 

Peabody's  Manual  of  the  Steam-engine  Indicator 12mo,     1  50 

Tables    of   the  Properties  of   Saturated   Steam   and 

Other  Vapors 8vo,     1  00 

"        Thermodynamics    of    the    Steam-engine    and    Other 

Heat-engines 8vo,     5  00 

Valve- gears  for  Steam-engines 8vo,    2  50 

Peabody  and  Miller.     Steam-boilers 8vo,    4  00 

Pray's  Twenty  Years  with  the  Indicator Large  8vo,    2  50 

Pupin's  Thermodynamics   of  Reversible   Cycles    in   Gases   and 

Saturated  Vapors.     (Osterberg.) 12mo,     1  25 

Reagan's  Locomotive  Mechanism  and  Engineering 12mo,    2  00 

Rontgen's  Principles  of  Thermodynamics.     (Du  Bois.) 8vo,     5  00 

Sinclair's  Locomotive  Engine  Running  and  Management.  .12mo,    2  00 
Smart's  Handbook  of  Engineering  Laboratory  Practice.  .12mo,    2  50 

Snow's  Steam-boiler  Practice 8vo,     3  00 

Spangler's    Valve-gears 8vo,    2  50 

Notes  on  Thermodynamics 12mo,     1  00 

Thurston's  Handy  Tables 8vo,     1  50 

Manual  of  the  Steam-engine 2  vols.,  8vo,  10  00 

Part  I.— History,  Structure,  and  Theory 8vo,     6  00 

Part  II. — Design,  Construction,  and  Operation 8vo,     6  00 

Thurston's  Handbook  of  Engine  and  Boiler  Trials,  and  the  Use 

of  the  Indicator  and  the  Prony  Brake 8vo,     5  00 

Stationary  Steam-engines 8vo,    2  50 

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tice   12mo,     1  50 

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Weisbach's  Heat,  Steam,  and  Steam-engines.     (Du  Bois.)..8vo,     5  00 

Whitham's  Steam-engine  Design 8vo,    5  00 

Wilson's  Treatise  on  Steam-boilers-     (Flather.) 16mo,     2  50 

Wood's    Thermodynamics,    Heat    Motors,     and    Refrigerating 

Machines   8vo,     4  00 

13 


MECHANICS  AND  MACHINERY. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

Bovey's  Strength  of  Materials  and  Theory  of  Structures.  .8 vo,  7  50 

Chorda!.— Extracts  from  Letters 12mo,  2  00 

Church's  Mechanics  of  Engineering 8vo,  6  00 

Notes  and  Examples  in  Mechanics 8vo,  2  00 

Compton's  First  Lessons  in  Metal- working 12mo,  1  50 

Compton  and  De  Groodt.    The  Speed  Lathe .  12mo,  1  50 

Cromwell's  Treatise  on  Toothed  Gearing 12mo,  1  50 

Treatise  on  Belts  and  Pulleys 12mo,  1  50 

Dana's   Text-book   of  Elementary   Mechanics   for   the    Use   of 

Colleges  and  Schools 12mo,  1  50 

Dingey's  Machinery  Pattern  Making 12mo,  2  00 

Dredge's  Record  of  the  Transportation  Exhibits  Building  of  the 

World's  Columbian  Exposition  of  1893 4to,  half  mor.,  5  00 

Du  Bois's  Elementary  Principles  of  Mechanics: 

Vol.  I.— Kinematics  8vo,  3  50 

Vol.  II.— Statics 8vo,  4  00 

Vol.  III.— Kinetics 8vo,  3  50 

Du  Bois's  Mechanics  of  Engineering.    Vol.  I Small  4to,  10  00 

Durley's  Elementary  Text-book  of  the  Kinematics  of  Machines. 

(In  preparation.) 

Fitzgerald's  Boston  Machinist 16mo,  1  00 

Flather's  Dynamometers,  and  the  Measurement  of  Power.  12mo,  3  00 

"        Rope    Driving 12mo,  2  00 

Hall's  Car  Lubrication 12mo,  1  00 

Holly's  Art  of  Saw  Filing 18mo,  75 

*  Johnson's  Theoretical  Mechanics 12mo,  3  00 

Jones's  Machine  Design: 

Part  I. — Kinematics  of  Machinery 8vo,  1  50 

Part  II. — Form,  Strength  and  Proportions  of  Parts ....  8vo,  3  00 
Kerr's  Power  and  Power  Transmission.     (In  preparation.) 

Lanza's  Applied  Mechanics 8vo,  7  50 

MacCord's  Kinematics;   or,  Practical  Mechanism 8vo,  5  00 

Velocity  Diagrams 8vo,  1  50 

Merriman's  Text-book  on  the  Mechanics  of  Materials 8 vo,  4  00 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  00 

Reagan's  Locomotive  Mechanism  and  Engineering 12mo,  2  00 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  00 

"       Text-book    of    Mechanical    Drawing    and    Elementary 

Machine  Design 8vo,  3  00 

Richards's  Compressed  Air 12mo,  1  50 

Robinson's  Principles  of  Mechanism 8vo,  3  00 

Sinclair's  Locomotive-engine  Running  and  Management ..  12mo,  2  00 

Smith's  Press-working  of  Metals 8vo,  3  00 

Thurston's   Treatise   on  Friction   and  Lost  Work   in  Machin- 
ery and  Mill  Work 8vo,  3  00 

"  Animal  as  a  Machine  and  Prime  Motor,  and   the 

Laws  of  Energetics 12mo,  1  00 

Warren's  Elements  of  Machine  Construction  and  Drawing.  .8vo,  7  50 
Weisbach's     Kinematics     and     the     Power    of     Transmission. 

(Hernnan— Klein.)    8vo,  5  00 

"  Machinery  of  Transmission  and  Governors.     (Herr- 

(man— Klein.)    8vo,  500 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  00 

"       Principles  of  Elementary  Mechanics 12mo,  1  25 

"       Turbines   8vo,  2  50 

The  World's  Columbian  Exposition  of  1893 4to,  1  OQ. 

14 


METALLURGY. 

Eglestorrs  Metallurgy  of  Silver,  Gold,  and  Mercury: 

Vol.  I -Silver 8vo,  7  50 

Vol.  II.— Gold  and  Mercury -JIVL&2 8vo>  7  50 

Keep's  Cast  Iron.     (In  preparation.) 

Kunhardt's  Practice  of  Ore  Dressing  in  Lurope 8vo,  1  50 

Le  Chatelier's  High-temperature  Measurements.     (Boudouard — 

Burgess.)  12mo,  3  00 

Metcalf s  Steel.    A  Manual  for  Steel-users 12mo,  2  00 

Thurston's  Materials  of  Engineering.    In  Three  Parts 8vo,  8  00 

Part  II.— Iron  and  Steel 8vo,  3  50 

Part  III. — A  Treatise  on  Brasses,  Bronzes  and  Other  Alloys 

and  Their  Constituents 8vo,  2  50 

MINERALOGY. 

Barringer's    Description    of    Minerals    of    Commercial    Value. 

Oblong,  morocco,  2  50 

Boyd's  Resources   of   Southwest   Virginia 8vo,  300 

"       Map  of  Southwest  Virginia Pocket-book  form,  2  00 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.)  .8vo,  4  00 

Chester's  Catalogue  of  Minerals 8vo,  paper,  1  00 

Cloth,  1  25 

"         Dictionary  of  the  Names  of  Minerals 8vo,  3  50 

Dana's  System  of  Mineralogy.' Large  8vo,  half  leather,  12  50 

"      First  Appendix  to  Dana's  New  "  System  of  Mineralogy." 

Large  8vo,  1  00 

"      Text-book  of  Mineralogy 8vo,  4  00 

"      Minerals  and  How  to  Study  Them 12mo,  1  50 

"      Catalogue  of  American  Localities  of  Minerals .  Large  8vo,  1  00 

"      Manual  of  Mineralogy  and  Petrography 12mo,  2  00 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Hussak's     The     Determination     of     Rock-forming     Minerals. 

(Smith.)    Small  8vo,  2  00 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of 

Mineral  Tests 8vo,  paper,  50 

Rosenbusch's  Microscopical  Physiography  of  the  Rock-making 

Minerals.      (Idding's.) 8vo,  500 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks . .  8vo,  2  00 
Williams's  Manual  of  Lithology 8vo,  3  00 

MINING. 

Beard's  Ventilation  of  Mines 12mo,  2  50 

Boyd's  Resources  of  Southwest  Virginia 8vo,  3  00 

"       Map  of  Southwest  Virginia Pocket-book  form,  2  00 

*  Drinker's     Tunneling,     Explosive     Compounds,     and     Rock 

Drills .4to,  half  morocco,  25  00 

Eissler's  Modern  High  Explosives 8vo,  4  00 

Goodyear's  Coal-mines  of  the  Western  Coast  of  the  United 

States 12mo,  250 

Ihlseng's  Manual  of  Mining 8vo,  4  00 

Kunhardt's  Practice  of  Ore  Dressing  in  Europe 8vo,  1  50 

O'DriscolTs  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  00 

Sawyer's  Accidents  in  Mines 8vo,  7  00 

Walke's  Lectures  on  Explosives 8vo,  4  00 

Wilson's  Cyanide  Processes 12mo,  1  50 

Wilson's  Chlorination  Process 12mo,  1  50 

15 


Wilson's  Hydraulic  and  Placer  Mining 12mo,  2  OO 

Wilson's  Treatise  on  Practical  and  Theoretical  Mine   Ventila- 
tion   12mo.  1  25 

SANITARY  SCIENCE. 

Fohvell's  Sewerage.     (Designing,  Construction  and  Maintenance.) 

8vo,  3  00 

Water-supply    Engineering 8vo.  4  00 

Fuertes's  Water  and  Public  Health 12mo.  1  50 

Water-filtration   Works 12mo,  2  50 

Gerhard's  Guide  to  Sanitary  House-inspection IGmo,  1  00 

Goodrich's  Economical  Disposal  of  Towns'  Refuse.  .  .Demy  8vo,  3  50 

Hazen's  Filtration  of  Public  Water-supplies 8vo,  3  00- 

Kiersted's  Sewage  Disposal 12mo,  1  25 

Mason's   Water-supply.     (Considered   Principally   from   a   San- 
itary Standpoint 8vo,  5  00 

"        Examination    of    Water.       (Chemical    and    Bacterio- 
logical.)      12mo,  1  25 

Merriman's  Elements  of  Sanitary  Engineering 8vo.  2  00 

Nichols's  Water-supply.     (Considered  Mainly  from  a  Chemical 

and  Sanitary  Standpoint.)      (1883.)   8vo,  2  50 

Ogden's  Sewer  Design 12mo,  2  00 

Richards's  Cost  of  Food.    A  Study  in  Dietaries 12mo,  1  00- 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sani- 
tary   Standpoint • 8vo,  2  00 

Richards's  Cost  of  Living  as  Modified  by  Sanitary  Science .  12mo,  1  00 

Rideal's  Sewage  and  Bacterial  Purification  of  Sewage 8vo,  3  50 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  00 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Woodhull's  Notes  on  Military  Hygiene 16mo,  1  50 

MISCELLANEOUS. 

Barker's  Deep-sea  Soundings 8vo,  2  Oft 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Ex- 
cursion   of    the    International    Congress    of    Geologists. 

Large  8vo,  1  50 

Ferrel's  Popular  Treatise  on  the  Winds 8vo,  4  00 

Haines's  American  Railway  Management 12mo,  2  50- 

Mott's  Composition,  Digestibility,  and  Nutritive  Value  of  Food. 

Mounted  chart,  1  25 

"      Fallacy  of  the  Present  Theory  of  Sound 16mo,  1  00 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute,   1824- 

1894. Small    8vo,  3  00 

Rotherham's  Emphasised  New  Testament Large  8vo,  2  00- 

Critical  Emphasised  New  Testament 12mo,  1  50 

Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

Totten's  Important  Question  in  Metrology 8vo,  2  50 

The  World's  Columbian  Exposition  of  1893 4to,  1  00 

Worcester  and  Atkinson.     Small  Hospitals,  Establishment  and 
Maintenance,  and  Suggestions  for  Hospital  Architecture, 

with  Plans  for  a  Small  Hospital 12mo,  1  25 

HEBREW    AND    CHALDEE    TEXT-BOOKS. 

Green's  Grammar  of  the  Hebrew  Language 8vo,  3  00 

"       Elementary  Hebrew   Grammar 12mo,  1  25 

Hebrew  Chrestomathy 8vo,  200 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament 

Scriptures.     (Tregelles.) Small  4to,  half  morocco.  5  00 

Letteris's  Hebrew  Bible . .  8vo,  2  25> 

16 


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UNIVERSITY  OF  CALIFORNIA  LIBRARY 


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